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A-B-C 

OF 

ELECTRICITY 




BY 



WILLIAM H. MEADOWCROFT 



HARPER & BROTHERS PUBLISHERS 
NEW YORK & LONDON 



% 



^ 



A-B-C of Electricity 

COPYRIGHT. 1888. 1909, BY WILLIAM H. MEADOWCROFT 



COPYRIGHT. 1915, BY HARPER a BROTHERS 

PRINTED IN THE UNITED STATES OF AMERICA 

PUBLISHED MAY. 1915 



E-P 

$6 t 



S± 



MAY 22 1915 



From the Laboratory of Thomas A. Edison 

Orange, N. J. 



Mr. W. H. Meadowcroft, 

New York City. 



DEAR SIR : 

I have read the MS. of your "A-B-C of 
Electricity " and find that the statements you have 
made therein are correct. Your treatment of the 
subject, and arrangement of the matter, have im- 
pressed me favorably. 

Yours truly, 

THOS. A. EDISON 



CONTENTS 



CHAP. PAGE 

Introduction to New Edition xi 

Preface xiii 

I 1 

II. Definitions 3 

III. f Magnetism 16 

IV. The Telegraph 23 

V. Wireless Telegraphy 33 

VI. The Telephone 40 

VII. Electric Light 54 

VIII. Electric Power 87 

IX. Batteries 95 

X. Conclusion 127 



INTRODUCTION 
TO NEW EDITION 

THE favor with which this book has 
been received has brought about the 
preparation of this new edition. The present 
volume has been enlarged by the addition 
of certain new material and it has been 
entirely reset. Some new illustrations have 
been made, and in its new dress the book, it 
is hoped, will be found to afford an even 
larger measure of usefulness. The principles 
of the science remain the same, but the 
author is glad of the opportunity to note 
certain developments in their application. 

W. H. M. 

Edison Laboratory, April , 1915. 



PREFACE 

WHILE there is no lack of most excel- 
lent text-books for the study of those 
branches of Electricity which are above the 
elementary stage, there is a decided need of 
text-books which shall explain, in simple 
language, to young people of, say, fourteen 
years and upward, a general outline of the 
science, as well as the ground-work of those 
electrical inventions which are to-day of such 
vast commercial importance. 

There is also a need for such a book among 
a large part of the adult population, for the 
reason that there have been great and radi- 
cal changes in this science since the time 
they completed their studies, and they have 
not the time to follow up the subject in the 
advanced books. 

As instances of those changes just spoken 
of, the electric light, telephone, and storage 
batteries may be mentioned, which have 
been developed during the last ten or twelve 
years, with the result of adding very many 



PREFACE 

features that were entirely new to electri- 
cians. 

With these ideas in view I have prepared 
this little volume. It is not intended, in the 
slightest degree, to be put forward as a scien- 
tific work, but it will probably give to many 
the information they desire without requir- 
ing too great a research into books which 
treat more extensively and deeply of this 
subject. 

W. H. M. 



A-B-C OF ELECTRICITY 



ABC OF ELECTRICITY 



WE now obtain so many of our comforts 
and conveniences by the use of elec- 
tricity that all young people ought to learn 
something of this wonderful force, in order to 
understand some of the principles which are 
brought into practice. 

You all know that we have the telegraph, 
the telephone, the electric light, electric mo- 
tors on street-cars, electric bells, etc., besides 
many other conveniences which the use of 
electricity gives us. 

Every one knows that, by the laws of multi- 
plication, twice two makes four, and that 
twice two can never make anything but four. 
Well, these useful inventions have been made 
by applying the laws of electricity in certain 
ways, just as well known, so as to enable us 
to send in a few moments a message to our 
i l 



A-B-C OF ELECTRICITY 

absent friends at any distance, to speak with 
them at a great distance, to light our houses 
and streets with electric light, and to do many 
other useful things with quickness and ease. 

But you must remember that we do not 
know what electricity itself really is. We 
only know how to produce it by certain 
methods, and we also know what we can do 
with it when we have obtained it. 

In this little book we will try to explain the 
various ways by which electricity is obtained, 
and how it is applied to produce the useful 
results that we see around us. 

We will try and make this explanation such 
that it will encourage many of you to study 
this very important and interesting subject 
more deeply. 

In the advanced books on electricity there 
are many technical terms which are some- 
what difficult to understand, but in this book 
it will only be necessary to use a few of the 
more simple ones, which it will be well for you 
to learn and understand before going further. 



II 

DEFINITIONS 

THE three measurements most frequently 
used in electricity are 

The Volt, 
The Ampere, 
The Ohm. 

We will explain these in their order. 

The Volt. — This term may be better un- 
derstood by making a comparison with some- 
thing you all know of. Suppose we have a 
tank containing one 
hundred gallons of 
water, and we want 
to discharge it 
through a half -inch 
pipe at the bottom 
of the tank. Sup- 
pose, further, that 
we wanted to make 
the water spout up- Fig. 1 




A-B-C OF ELECTRICITY 



ward, and for this purpose the pipe was bent 
upward as in Fig. 1. 

If you opened the tap the water would 
spout out and upward as in Fig. 1. 

The cause of its spouting upward would be 
the weight or pressure 
of the water in the 
tank. This pressure 
is reckoned as so many 
pounds to the square 
inch of water. 

Now, if the tank 
were placed on the roof 
of the house and the 
pipe brought to the 
ground as shown in 
Fig. 2, the water would 
spout up very much 
higher, because there 
would be many more 
pounds of pressure on 
account of the height 
of the pipe. 
So, you see, the force or pressure of water 
is measured in pounds, and, therefore, a 
pound is the unit of pressure, or force, of 
water. Now, in electricity the unit of press- 
ure, or force, is called a volt. 

This word "volt" does not mean any 

4 




Fig. 2 



DEFINITIONS 

weight, as the word "pound" weight does. 
You all know that if you have a pound of 
water you must have something to hold it, 
because it has weight, and, consequently, oc- 
cupies some space. But electricity itself has 
no weight and therefore cannot occupy any 
space. 

When we desire to carry water into a house 
or other building we do so by means of hollow 
pipes, which are usually made of iron. This 
is the way that water is brought into houses 
in cities and towns, so that it may be drawn 
and used in any part of a dwelling. Now, 
the principal supply usually comes from a 
reservoir which is placed up on high ground 
so as to give the necessary pounds of press- 
ure to force the water up to the upper part 
of the houses. If some arrangement of this 
kind were not made we could get no water in 
our bedrooms, because, as you know, water 
will not rise above its own level unless by 
force. 

The water cannot escape as long as there 
are no holes or leaks in the iron pipes, but 
if there should be the slightest crevice in them 
the water will run out. 

In electricity we find similar effects. 

The electricity is carried into houses by 
means of wires which are covered, or insu- 



A-B-C OF ELECTRICITY 

lated, with various substances, such, for in- 
stance, as rubber. Just as the iron of the 
pipes prevents the water from escaping, the 
insulation of the wire prevents the escape of 
the electricity. 

Now, if we were to cause the pounds of 
pressure of water, in pipes of ordinary thick- 
ness, to be very greatly increased, the pipes 
could not stand the strain and would burst 
and the water escape. So it is with elec- 
tricity. If there were too many volts of 
pressure the insulation would not be sufficient 
to hold it and the electricity would escape 
through the covering, or insulation, of the 
wire. 

It is a simple and easy matter to stop the 
flow of water from an ordinary faucet by 
placing your finger over the opening. As the 
water cannot then flow, your finger is what 
we will call a non-conductor and the water 
will be retained in the pipe. 

We have just the same effects in electricity. 
If we place some substance which is practi- 
cally a non-conductor, or insulator, such as 
rubber, around an electric wire, or in the 
path of an electric current, the electricity, 
acted upon by the volts of pressure, cannot 
escape, because the insulation keeps it from 

doing so, just as the iron of the pipe keeps the 
6 



DEFINITIONS 

water from escaping. Thus, you see, the 
volt does not itself represent electricity, but 
only the pressure which forces it through the 
wire. 

There are other words and expressions in 
electricity which are sometimes used in con- 
nection with the word "volt." These words 
are "pressure" and "intensity." We might 
say, for instance, that a certain dynamo 
machine had an electro-motive force of 110 
volts; or that the intensity of a cell of a 
battery was 2 volts, etc. 

We might mention, as another analogy, 
the pressure of steam in a boiler, which is 
measured or calculated in pounds, just as the 
pressure of water is measured. So, we might 
say that 100 pounds steam pressure used 
through the medium of a steam-engine to 
drive a dynamo could thus be changed to 
electricity at 100 volts pressure. 

The Ampere. — Now, in comparing the 
pounds pressure of water with the volts of 
pressure of electricity we used as an illustra- 
tion a tank of water containing 100 gallons, 
and we saw that this water had a downward 
force or pressure in pounds. Let us now see 
what this pressure was acting upon. 

It was forcing the quantity of water to 
spout upward through the end of the pipe. 



A-B-C OF ELECTRICITY 

Now, as the quantity of water was 100 
gallons, it could not all be forced at once out 
of the end of the pipe. The pounds pressure 
of water acting on the 100 gallons would 
force it out at a certain rate, which, let us say, 
would be one gallon per minute. 

This would be the rate of the flow of water 
out of the tank. 

Thus, you see, we find a second measure- 
ment to be considered in discharging the 
water-tank. The first was the force, or 
pounds of pressure, and the second the rate 
at which the quantity of water was being dis- 
charged per minute by that pressure. 

This second measurement teaches us that 
a certain quantity will pass out of the pipe in a 
certain time if the pressure is steady, such 
quantity depending, of course, on the size or 
friction resistance of the pipe. 

In electricity the volts of pressure act so as 
to force the quantity of current to flow through 
the wires at a certain rate per second, and the 
rate at which it flows is measured in amperes. 
For instance, let us suppose that an electric 
lamp required a pressure of 100 volts and a 
current of one ampere to light it up, we should 
have to supply a current of electricity flowing 
at the rate of one ampere, acted upon by an 

electro-motive force of 100 volts. 

8 



DEFINITIONS 

You will see, therefore, that while the volt 
does not represent any electricity, but only 
its pressure, the ampere represents the rate of 
flow of the current itself. 

You should remember that there are several 
words sometimes used in connection with the 
word " ampere" — for instance, we might say 
that a lamp required a " current" of one am- 
pere or that a dynamo would give a " quan- 
tity" of 20 amperes. 

The Ohm. — You have learned that the 
pressure would discharge the quantity of water 
at a certain rate through the pipe. Now, sup- 
pose we were to fix two discharge-pipes to the 
tank, the water would run away very much 
quicker, would it not? If we try to find a 
reason for this, we shall see that a pipe can 
only, at a given pressure, admit so much 
water through it at a time. 

Therefore, you see, this pipe would present 

a certain amount of resistance to the passage 

of the total quantity of water, and would only 

allow a limited quantity at once to go through. 

But, if we were to attach two or more pipes 

to the tank, or one large pipe, we should 

make it easier for the water to flow, and, 

therefore, the total amount of resistance to 

the passage of the water would be very much 

less, and the tank would quickly be emptied. 
9 



A-B-C OF ELECTRICITY 

Now, as you already know, water has sub- 
stance and weight and therefore occupies 
some space, but electricity has neither sub- 
stance nor weight, and therefore cannot oc- 
cupy any space; consequently, to carry elec- 
tricity from one place to another we do not 
need to use a pipe, which is hollow, but we use 
a solid wire. 

These solid wires have a certain amount of 
resistance to the passage of the electricity, 
just as the water-pipe has to the water, and 
(as it is in the case of the water) the effect of 
the resistance to the passage of electricity is 
greater if you pass a larger quantity through 
than a smaller quantity. 

If you wanted to carry a quantity of elec- 
tricity to a certain distance, and for that 
purpose used a wire, there would be a certain 
amount of resistance in that wire to the pas- 
sage of the current through it; but if you 
used two or more wires of the same size, or one 
large wire, the resistance would be very much 
less and the current would flow more easily. 

Suppose that, instead of emptying the 
water-tank from the roof through the pipe, 
we had just turned the tank over and let the 
water all pour out at once down to the 
ground. That would dispose of the water 
very quickly and by a short way, would it 
10 



DEFINITIONS 

not? That is very easy to be seen, because 
there would be no resistance to its passage to 
the ground. 

Well, suppose we had an electric battery 
giving a certain quantity of current, say 
five amperes, and we should take a large wire 
that would offer no resistance to that quan- 
tity and put it from one side of the battery to 
the other, a large current would flow at once 
and tend to exhaust the battery. This is 
called a short circuit because there is little or 
no resistance, and it provides the current with 
an easy path to escape. Remember this, that 
electricity always takes the easiest path. It will 
take as many paths as are offered, but the 
largest quantity will always take the easiest. 

As the subject of resistance is one of the 
most important in electricity, we will give you 
one more example, because if you can obtain 
a good understanding of this principle it will 
help you to comprehend the whole subject 
more easily in your future studies. 

We started by comparison with a tank 

holding 100 gallons of water, discharging 

through a half-inch pipe, and showed you 

that the pounds of pressure would force the 

quantity of gallons through the pipe. When 

the tap was first opened the water would 

spout up very high, but as the water in the 
11 



A-B-C OF ELECTRICITY 

tank became lower the pressure would be 
less, and, consequently, the water would not 
spout so high. 

So, if it were desired to keep the water 
spouting up to the height it started with, we 
should have to keep the tank full, so as to 
have the same pounds of pressure all the 
time. But, if we wanted the water to spout 
still higher we should have to use other means, 
such as a force-pump, to obtain a greater 
pressure. 

Now, if we should use too many pounds 
pressure it would force the quantity of water 
more rapidly through the pipe and would 
cause the water to become heated because of 
the resistance of the pipe to the passage of 
that quantity acted upon by so great a 
pressure. 

This is just the same in electricity, except 
that the wire itself would become heated, 
some of the electricity being turned into heat 
and lost. If a wire were too small for the 
volts pressure and amperes of current of 
electricity the resistance of such wire would 
be overcome, and it would become red-hot 
and perhaps melt. Electricians are therefore 
very careful to calculate the resistance of the 
wires they use before putting them up, espe- 
cially when they are for electric lighting, in 
12 



DEFINITIONS 

order to make allowances for the amperes of 
current to flow through them, so that but 
little of the electricity will be turned into 
heat and thus rendered useless for their 
purpose. 

The unit of resistance is called the ohm 
(pronounced like "home" without the "h"). 

All wires have a certain resistance per foot, 
according to the nature of the metal used and 
the size of the wire — that is to say, the finer 
the wire the greater number of ohms resist- 
ance it has to the foot. 

Water and electricity flow under very sim- 
ilar conditions — that is to say, each of them 
must have a channel, or conductor, and each 
of them requires pressure to force it onward. 
Water, however, being a tangible substance, 
requires a hollow conductor; while electricity, 
being intangible, will flow through a solid 
conductor. The iron of the water-pipe and 
the insulation of the electric wire serve the 
same purpose — namely, that of serving to 
prevent escape by reason of the pressure 
exerted. 

There is another term which should be 
mentioned in connection with resistance, as 
they are closely related, and that is opposi- 
tion. There is no general electrical term of 
this name, but, as it will be most easily under- 

13 



A-B-C OF ELECTRICITY 

stood from the meaning of the word itself, we 
have used it. 

Let us give an example of what opposition 
would mean if applied to water. Probably 
every one knows that a water-wheel is a wheel 
having large blades, or " paddles," around its 
circumference. 

When the water, in trying to force its pas- 
sage, rushes against one of these paddles it 
meets with its opposition, but overcomes it 
by pushing the paddle away. This brings 
around more opposition in the shape of an- 
other paddle, which the water also pushes 
away. And so this goes on, the water over- 
coming this opposition and turning the wheel 
around, by which means we can get water to 
do useful work for us. 

You must remember, however, that it is 
only by putting opposition in the path of a 
pressure and quantity of water that we can 
get this work. 

The same principle holds good in electricity. 
We make electricity in different ways, and 
in order to obtain useful work we put in its 
path the instruments, lamps, or machines 
which offer the proper amount of resistance, 
or opposition, to its passage, and thus obtain 
from this wonderful agent the work we desire 
to have done. 

14 



DEFINITIONS 

You have learned that three important 
measurements in electricity are as follows: 

The volt is the practical unit of measure- 
ment of pressure; 

The ampere is the practical unit of measure- 
ment of the rate of flow; and 

The ohm is the practical unit of measure- 
ment of resistance. 



Ill 

MAGNETISM 

NOW we will try to explain to you some- 
thing about magnets and magnetism. 
There are very few boys who have not seen 
and played with the ordinary magnets, 
shaped like a horseshoe, which are sold in all 
toy-stores as well as by those who sell elec- 
trical goods. 

Well, you know that these magnets will 
attract and hold fast anything that is made 
of iron or steel, but they have no effect on 
brass, copper, zinc, gold, or silver, yet there 
is nothing that you can see which should 
cause any such effect. You will notice, then, 
that magnetism is like electricity; we cannot 
see it, but we can tell that it exists, because it 
produces certain effects. And here is another 
curious thing — magnetism produces electric- 
ity, and electricity produces magnetism. 
This seems to be a very convenient sort of a 
family affair, and it is owing to this close re- 

16 



MAGNETISM 



lation that we are able to obtain so many 
wonderful things by the use of electricity. 

We shall now show you how electricity 
produces magnetism, and, when we come to 
the subject of electric lighting we will explain 
how magnetism produces electricity. 

The easiest way to show how electricity 
makes magnetism is to find out how magnets 
are made. Suppose 
we wanted to make a 
horseshoe magnet, just 
mentioned above; we 
would take a piece of 
steel and wind around 
it some fine copper 
wire, commencing on 
one leg of the horse- 
shoe and winding 
around until we came 
to the end of the other 
leg. Then we should have two ends of wire 
left, as shown in the sketch. (Fig. 3.) 

We connect these two ends with an electric 
battery, giving, say, two volts, and then the 
amperes of current of electricity will travel 
through the wire, and in doing so has such 
an influence on the steel that it is converted 
into a magnet, such as you have played 
with. The current is " broken" — that is to 

2 17 




Fig. 3 



A-B-C OF ELECTRICITY 

say, it is shut off several times in making a 
magnet of this kind, and then the wire is taken 
away from the battery and is unwound from 
the steel horseshoe, leaving it free from wire, 
just as you have seen it. This horseshoe is 
now a permanent magnet — that is, it will 
always attract and hold pieces of iron and 
steel. 

Now, if you were to do the same thing 
with a horseshoe made of soft iron instead of 
steel it would not be a magnet after you 
stopped the current of electricity from going 
through the wires, although the piece of iron 
would be a stronger magnet while the elec- 
tricity was going through the wire around it. 

The steel magnet is called a permanent 
magnet, and its ends, or "poles," are named 
North and South. There is usually a loose 
piece of steel or iron, called an "armature," 
put across the ends, which has the peculiar 
property of keeping the magnetism from be- 
coming weaker, and thereby retaining the 
strength of the magnet. The strongest part 
of the magnet is at the poles, while, at the 
point marked + (which is called the neutral 
point) there is scarcely any magnetism. 

It will be well to remember the object of the 
armature as we shall meet it again in describ- 
ing dynamo machines. 

18 



MAGNETISM 



The magnets made of iron are called electro- 
magnets because they exhibit magnetism only 
when the amperes of current of electricity 
are flowing around them. They also have 
two poles, north and south, as have perma- 
nent magnets. Elec- 
tromagnets are used 
in nearly all electrical 
instruments, not only 
because they are 
stronger than perma- 
nent magnets, but be- 
cause they can be made 
to act instantly by 
passing a current of 
electricity through 
them at the most con- 
venient moment, as 
you will see when we 
explain some of the 
electrical instruments which are used to pro- 
duce certain effects. (Fig. 4.) 

Of course there are a great many different 
shapes in which magnets are made. The 
simplest is the bar magnet, which is simply a 
flat or round piece of iron or steel. Suppose 
you made a magnet of a flat piece of steel and 
put on top of it a sheet of paper, and then 
threw on the paper some iron filings, you 

19 




Fig. 4 



A-B-C OF ELECTRICITY 



would see them arrange themselves as is 
shown in the following sketch. (Fig. 5.) 

The filings would always arrange them- 
selves in this shape, no matter how large or 
small the magnets were. And, if you were 

to cut it into two or 
half a dozen pieces, 
each piece would 
have the same effect. 
This shows you that 
each piece would it- 
self become a mag- 
net and would -have 
its poles exactly as 
the large one had. 

Now, we have an- 
other curious thing 
to tell you about magnets. If you present the 
north pole of a magnet to the south pole of an- 
other magnet, they will attract and hold fast 
to each other, but if you present a south pole 
to another south pole, or a north pole to a 
north pole, they will repel each other, and 
there will be no attraction. You can per- 
form some interesting experiments by reason 
of this fact. We will give you one of them. 
Take, say, a dozen needles and draw them 
several times in the same direction across the 
ends of a magnet so that they become mag- 

20 




MAGNETISM 

netized. Now stick each needle half-way 
through a piece of cork, and put the corks, 
with the needles sticking through them, into 
a bowl of water. Then take a bar magnet 
and bring it gradually toward the middle of 
the bowl and you will see the corks advance 
or back away from the magnet. If the ends 
of the needles sticking up out of the water 
are south poles and the end of the magnet 
you present is a north pole, the needles will 
come to the center; but will go to the side 
of the bowl if you present the south pole. 
You can vary this pretty experiment by 
turning up the other ends of part of the 
needles. 

You will remember that when we explained 
what " resistance" meant, we told you that 
electricity would always take the easiest path, 
and while part of it will flow in a small wire, 
the largest portion will take an easier path 
if it can get to something larger that is a 
metallic substance. Electricity will only flow 
easily through anything that is made of metal. 
You will also remember that you learned that 
when electricity took a short cut to get away 
from its proper path it was called a short 
circuit. 

All this must be taken into consideration 
when magnets are being made. In the first 

21 



A-B-C OF ELECTRICITY 

place, the wire we wind around steel or iron 
to make magnets must always be covered 
with an insulator of electricity. Magnet wire 
is usually covered with cotton or silk. If it 
were left bare, each turn of the wire would 
touch the next turn, and so we should make 
such an easy path for the electricity that it 
would all go back to the battery by a short 
circuit, and then we would get no magnetic 
effect in the steel or iron. The only way we 
can get electricity to do useful work for us is to 
put some resistance or opposition in its way. 
So you see that if we make it travel through 
the wire around the iron or steel, there is just 
enough resistance or opposition in its way 
to give it work to get through the wire, and 
this work produces the peculiar effect of 
making the iron or steel magnetic. 

The covering on the wire, as you will re- 
member, is called "insulation." 



IV 

THE TELEGRAPH 

EVERY one knows how very convenient 
the telegraph is, but there are not many 
who think how wonderful it is that we can 
send a message in a few seconds of time to a 
distant place, even though it were thousands 
of miles away. And yet, though the present 
system of telegraphing is a wonderful one, 
the method of sending a telegram is simple 
enough. The apparatus that is used in send- 
ing a telegram is as follows: 

The Battery. 
The Wire. 

The Telegraph Key. 
The Sounder. 

The different kinds of electric batteries 
will be mentioned afterward, so we will not 
stop now to describe them, but simply state 
that a battery is used to produce the neces- 
sary electricity. As you all know what wire 

23 



A-B-C OF ELECTRICITY 

is, there is no necessity of describing it 
further. 

The telegraph key is shown in the sketch 
below. (Fig. 6.) 




Fig. 6 

This instrument is usually made of brass, 
except that upon the handle there is the little 
knob which is of hard rubber. The handle, 
or lever, moves down when this knob is 
pressed, and a little spring beneath pushes 
it up again when let go. You will see a 
second smaller knob, the use of which we will 
explain later. 

The sounder is shown on the following 
page. (Fig. 7.) ^ 

The part consisting of the two black pil- 
lars is an electromagnet, and across the top 
of these pillars is a piece of iron called the 
" armature," which is held up by a spring. 

24 



THE TELEGRAPH 

Now let us see how the battery and wire 
are placed in connection with these instru- 
ments. You have seen that we usually have 
two wires for the electricity to travel in, one 
wire for it to leave the battery, and the other 




Fig. 7 



to return on. But you will easily see that 
if two wires had to be used in telegraphing it 
would be a very expensive matter, especially 
when they had to be carried thousands of 
miles. So, instead of using a second wire, 
we use the earth to carry back the electricity 
to the battery, because the earth is a better 
conductor even than wire. Although a quan- 
tity of ground equal in size to the wire would 
offer thousands of times greater resistance 
than the wire, yet, owing to the great body 

25 



A-B-C OF ELECTRICITY 

of our earth, its total resistance is even less 
than any telegraph wire used. 

When two electric wires are run from a 
battery and connected together through some 
instrument, this is called a "circuit," because 
the electricity has a path in which it can 
travel back to the battery. This would be 
a "metallic" circuit; but when one wire only 
is used, and the other side of the battery is 
connected with the earth, it is called a 
"ground" or "earth" circuit, because the 
electricity returns through the earth. 

If you look at this sketch (Fig. 8) you will 
see how the telegraph instruments are con- 



New"Vork 




V//J 

Battery Earth 



nected and will then be able to understand 
how a message can be sent. 

Here we have two sets of telegraph ap- 

26 



THE TELEGRAPH 

paratus, one of which, let us say, is in New 
York and the other in Philadelphia. 

You will see that one wire from the bat- 
tery is connected with the earth, and the 
other wire with the sounder. Another wire 
goes from the sounder to one leg of the key 
so as to make the brass base of the key part 
of the circuit. The other leg of the key is 
" insulated" from the brass base by being 
separated therefrom with some substance 
which will not carry electricity, such, for 
instance, as hard rubber. 

We will suppose that there is already a 
wire strung up on poles between New York 
and Philadelphia, and that the key, sounder, 
and battery in the latter city are connected 
in the same way as those in New York. 

Now, to enable us to send a message from 
one city to the other we must connect the 
ends of the wires to the instruments in each 
city; so we connect one end to the insulated 
leg of the key in New York, and the other 
end to the insulated leg of the key in Phila- 
delphia. 

Everything is now completed, and, as soon 

as we find out what is the use of that part 

of the key that has a little round, black 

handle, we shall be ready to start. This is 

called the " switch." 

27 



A-B-C OF ELECTRICITY 

If you will look once more at the picture 
of the key you will see under the long handle 
(or lever) a little point which the lever will 
touch when it is pressed down. Now this 
little point is part of that insulated leg, and, 
therefore, this point is also insulated from 
the base. If a current of electricity were 
sent along the wire it could not get any 
farther than this point unless we put in some 
arrangement to complete the path, or cir- 
cuit, for it to travel in. We therefore put 
in the switch. 

One end of the switch (which is made of 
brass with a rubber handle) is fastened on 
the base of the key, so that it may be moved 
to the right or left. The other end, when the 
switch is moved to the left (or " closed"), 
touches a piece of brass fastened to the little 
point we have mentioned, and so makes a 
free path for the electricity to go through 
the base of the key and through the wire to 
the sounder, and from there to the battery, 
and so back to the earth. This switch must 
be opened before the sounder near it will 
respond to its neighboring key. 

Now we are ready to send a message. 
Suppose we want to send a telegram from 
New York to Philadelphia. The operator 
in New York opens his switch and presses 

,28 



THE TELEGRAPH 

down his key several times. The switch on 
the Philadelphia key being closed, the elec- 
tricity goes through to the sounder, and, this 
being made an electromagnet by the current 
passing through the wire, the iron armature 
is attracted by the magnetism and drawn 
down to the magnet with a snap. It will 
stay there as long as the New York operator 
keeps his lever pressed down, but, when he 
allows it to spring up, there is no current 
passing through the Philadelphia sounder 
and there is no magnetism, consequently the 
armature springs up again with a click. 

As often as the operator presses down his 
key lever and lets it spring up again, the same 
action takes place in the sounder, and it 
makes that click, click, which you have heard 
if you have ever seen telegraph instruments 
in operation. 

Let us continue, however, to send our 
message. The New York operator, having 
pressed down his key several times to signal 
the Philadelphia operator, closes his switch 
to receive the answer from Philadelphia. The 
operator in the latter city then opens his 
switch and presses down his key several 
times, which makes the New York sounder 
click, in the same way, to let the operator 
there know that he is ready to receive the 

29 



A-B-C OF ELECTRICITY 

message. He then closes his switch and re- 
ceives the telegram which the New York 
operator sends after opening his key. 

Telegraphic messages are sent and received 
in this way and are read by the sound of the 
clicks. 

These sounds may be represented on paper 
by dots, dashes, and spaces. For instance, 
if you press down the key and let it spring 
back quickly, that would represent a dot. 
If you press down the key and hold it a little 
longer before letting it spring up again, it 
would represent a dash. A space would be 
represented by waiting a little while before 
pressing down the key again. 

We show you below the alphabet in these 
dots, dashes, and spaces, and these are the 
ones now used in sending all telegraphic 
messages. 



A 

urn 


B 
fllll 


c 

■■ ■ 


■II 


E 

■ 


F 
■■1 


G 


H 


I 

■■ ■ 


J 

MM 


K 

wmmm 


L 


M 


N 


O 
IB 


P 
■■■■■ 


Q 

■■■■ 


■ ■■ 


S 

■■■ 


T 


U 

HJffl 


V 
Iff* 


W 

MM 


X 


Y 

HI H 

30 


2 
1 Ml 


■ . 


& 

■ ■■■ 



THE TELEGRAPH 

Thus, you see, if you were telegraphing 
the word "and" you would press down your 
key and let it return quickly, then press down 
again and return after a longer pause, which 
would give the letter A; then slowly and 
quickly, which would be N; then slowly and 
twice quickly, which would be D. 

Any persevering boy can learn to operate 
a telegraph instrument by a little study and 
regular practice; and, as complete learner's 
sets can be purchased very cheaply, this 
affords a pleasant and useful recreation for 
boys. 

There are many cases where two boys liv- 
ing near each other have a set of telegraph 
instruments in their homes and run a wire 
from one house to the other, thus affording 
many hours of pleasant and profitable amuse- 
ment. 

In giving the above explanation of tele- 
graphing we have described only the simple 
and elementary form. In large telegraph 
lines, such as those of the Western Union, 
there are many more additional instruments 
used, which are very complicated and diffi- 
cult to understand; such, for instance, as 
the quadruplex, by which four distinct mes- 
sages can be sent over the same wire at the 
same time. We have, therefore, described 

31 



A-B-C OF ELECTRICITY 

only the simplest form in order to give the 
general idea of the working of the telegraph 
by electromagnetism, which is the principle 
of all telegraphing. 

When you study electricity more deeply 
you will find this subject and the many dif- 
ferent instruments very interesting and won- 
derful. . 



V 

WIRELESS TELEGRAPHY 

IF it has seemed extraordinary to you that 
only one wire should be necessary for 
sending a message by the electric telegraph, 
and that our earth can be used instead of a 
second wire, how much more wonderful it is 
to realize that in these days we can exchange 
telegraphic messages with different points 
without any connecting wires at all between 
them, even though the places be many hun- 
dred miles apart. Thus, two ships on the 
ocean, entirely out of sight of each other, 
may intercommunicate, or may telegraph to 
or receive despatches from a far-distant shore; 
indeed, telegraphy without wires has been 
accomplished across the Atlantic Ocean. In 
the language of the day, this is called " wire- 
less telegraphy," although it is more correct 
to think of it as aerial, or space, telegraphy. 
As you will naturally want to know how this 

3 33 



A-B-C OF ELECTRICITY 

is effected, we will try to explain the main 
principles in a simple manner. 

If you drop a stone into a quiet pond, you 
will see the water form into ring-like waves, 
or ripples, which travel on and on until they 
die away in the far distance. These waves 
are caused, as we have seen, by a disturb- 
ance of the body of water. 

Probably you have already learned in 
school that all known space is said to be 
filled with a medium called "ether," and that 
this medium is so exceedingly thin that it 
penetrates, or permeates, everything, so that 
it exists in the densest bodies as well as in 
free space. For the sake of obtaining a clear 
idea of this theory we may imagine that the 
ether envelops and permeates every thing in 
the entire universe. Hence we can easily 
realize that, although we cannot see or feel 
the ether, any disturbance of it will set' it in 
wavelike motion. 

Modern science accounts for light, radiant 
heat, and electrical phenomena by reason of 
wavelike disturbances, vibrations, or pulsa- 
tions of this ether. Thus, if you should strike 
a light, the ether would be disturbed, caus- 
ing waves to form, which, like the waves in 
the water, would travel in every direction. 
When these waves reached the eyes of an- 

34 



WIRELESS TELEGRAPHY 

other person within seeing distance, that 
person's eyes would be so acted upon by the 
waves that he would see the light which you 
had made, and would see it instantly, for 
light waves travel about 186,000 miles per 
second. 

So, if you create an electrical disturbance, 
the same kind of an effect will be produced; 
that is to say, waves in the ether will be 
created, or propagated, and will travel on 
and on in every direction. Now, if some 
form of electrical appliance can be made that 
will be of the right kind to respond to them 
(as the eye responds to light rays), these elec- 
tric waves can be made practically useful for 
transmitting messages through space. This 
is just what has been done, and we will now 
give you a brief general description of one 
kind of apparatus used. 

For "sending," or "transmitting," as it is 
usually termed, there is used an induction- 
coil, having rather large brass balls on the 
secondary terminals; suitable batteries, a 
condenser, a Morse telegraph key, and an 
"aerial," or wire which is carried away up 
into the air vertically, and is made fast to 
a pole or special tower. When these are 
connected properly, the closing of the cir- 
cuit with the key will cause sparks to jump 

35 



A-B-C OF ELECTRICITY 

between the brass balls. This electrical 
discharge, or oscillation, is carried by the 
aerial into the upper air and causes intense 
pulsations in the ether, which set up waves 
as already mentioned. If the circuit is 
opened again the disturbance ceases. So, 
by alternately closing and opening the cir- 
cuit, the Morse characters can be imitated. 
But how can these signals be received by 
the man for whom they are intended, who 
may be a hundred miles or more away? He 
has a " receiving" set, consisting of a sensi- 
tive relay, batteries, resistance-coils, a Morse 
register, an aerial, and a special device called 
a " coherer." This is the important part of 
the whole set, because it is sensitive to the 
electrical waves. It consists of a little glass 
tube about as large around as an ordinary 
lead-pencil, and perhaps two inches long. In 
the tube are two metallic plugs, each having 
a wire attached so that one wire projects 
from each end of the tube. The plugs are 
separated inside the tube by a very small 
space, and in this space are some metal 
filings. One wire from the coherer is con- 
nected to the aerial and the other to the 
ground. When there are no electrical ether 
waves to influence them, these filings, being 
loosely separated, are at rest and offer high 

36 



WIRELESS TELEGRAPHY 

resistance; but when the ether is disturbed 
by electrical vibrations and the waves arrive 
at the coherer (through the aerial), these 
filings are drawn together, or cohere. This 
lowers their resistance and they become a 
better conductor. Now, the coherer wires 
are also connected through a battery to the 
relay, which in turn is connected through 
another battery to a Morse register. There- 
fore, when the filings become a conductor, 
the current flows through them and the 
circuit to the relay is closed. That at- 
tracts an armature which closes the cir- 
cuit of the Morse register and thus marks 
the electrical impulse on a strip of paper 
tape. In the mean time, a restoring de- 
vice, called a "decoherer," operated also 
by the relay circuit, has tapped upon the 
coherer, thus shaking the filings loose again, 
so that they are ready to cohere again 
and register another impulse, or character. 
Thus, by pressing the key at the trans- 
mitting end for long or short periods, to 
represent Morse characters, long and short 
waves are propagated in the ether and are 
received and recorded at the receiving end 
through the coherer and other parts of the 
receiving set. In this way telegraphic mes- 
sages are sent and received through space, 

37 



A-B-C OF ELECTRICITY 

between points separated by hundreds or 
thousands of miles. 

We have tried to describe to you the gen- 
eral principles underlying the art of wireless 
telegraphy as plainly as possible, using for 
illustration the simplest kind of apparatus 
employed for the practical sending and re- 
ceiving of messages. At the present day 
there are several systems in actual practice, 
and with the growth of the art there have 
been many elaborations of apparatus that 
have come into use. For instance, the co- 
herer is not as much used as formerly. In 
its place there are employed several kinds of 
" wave-detectors" as they are now termed, 
and in many of the systems the electrical pul- 
sations are generated by a dynamo-machine 
instead of batteries. Then, again, instead of the 
messages being recorded by a Morse register 
at the receiving end, the operator receives 
them by means of a telephone receiver, 
through which he hears the Morse characters 
and writes them down in words as he hears 
them. Generally the aerial, or "antennae," 
as it is sometimes named, consists of several 
wires, sometimes a large number, carried to 
a considerable height. 

There are a great many other details which 
might be written to explain all the compli- 

38 



WIRELESS TELEGRAPHY 

cated apparatus which is used in some of the 
systems, but it is not intended in this book 
to offer more than a general explanation of 
main principles. We must leave it to you 
to study the details elsewhere if you so de- 
sire after you have read these pages. 



VI 

THE TELEPHONE 

YOU probably all know that the telephone 
is an electrical instrument by which one 
person may talk to another who is at a 
distance. Not only can we talk to a per- 
son who is in a different part of the city, but 
such great improvements have been made in 
these instruments that we can talk through 
the telephone to a person in another city, 
even though it be hundreds of miles away. 

The main principle of the telephone is 
electromagnetism, as in the telegraph, but 
there are other important points in addition 
to those we mentioned in describing the 
latter. 

Let us take first the 

INDUCTION-COIL 

You will remember that an electromagnet 
is made by winding many turns of wire around 
40 



THE TELEPHONE 

a piece of iron and sending a current of elec- 
tricity through this wire. 

Now, suppose this current of electricity 
was being supplied by two cells of a battery. 
If you took in your hands the wires coming 
from these two cells, giving, say, four volts, 
you could not feel any shock; but if you 
were to take hold of the ends of the wires on 
the electromagnet and separate them while 
this same current was going through, you 
would get a decided shock. 

This separation would "break" the cir- 
cuit, and the reason you would get a shock 
is that, while the electricity is acting on the 
wire, the iron itself is magnetized, and on 
breaking the circuit reacts upon the wire, 
producing for a moment more volts of press- 
ure in every turn of it. Thus, you see, this 
weak pressure of electricity as it travels 
through the wire can yet produce, through its 
magnetism, strong momentary effects, but 
you cannot feel it unless you break the circuit 

HOW THE INDUCTION-COIL IS MADE 

The object of the induction-coil is to pro- 
duce high intensity, or pressure, from a com- 
paratively weak pressure and large current 
of electricity; so, if we add still more wire, 
41 



A-B-C OF ELECTRICITY 

the magnet has a larger number of turns to 
act upon and thus makes a very strong 
pressure, or large number of volts, but a 
lesser number of amperes. 

Instead of taking one piece of iron, as we 
would for an ordinary electromagnet, we 
take a bundle of iron wires in making an 
induction-coil, as these give a stronger effect. 
Around this bundle of wires we wrap many 
turns of insulated copper wire. This is called 
the primary coil, and the ends of this wire 
are to be attached to the battery. 

On top of, or over, this primary coil we 

wrap a great 
many turns of 
very fine wire, of 
which, as it is so 
fine, a great 
length can be 
used. This is 
Fig. 9 called the second- 

ary coil, and it is 
in this coil that the volts, or pressure, of elec- 
tricity become strongest. 

Above we show you a sketch of an induc- 
tion-coil. (Fig. 9.) 

At the left-hand side of the cut is a " cir- 
cuit-breaker ," which is simply a piece of 
iron (armature) on a spring placed opposite 

42 




THE TELEPHONE 

the iron core. This armature is made a part 
of the wire leading to the primary coil. When 
the current from the battery is sent through 
the wires, the core becomes magnetized and 
draws this armature away from a fixed con- 
tact point, thus breaking the circuit, but 
the spring pulls it back, again completing 
the circuit, and so it keeps going back and 
forth very rapidly with a br-r-r-ing sound. 

If you were now to take hold of the ends 
of the secondary coil you would get a con- 
tinuous series of quick shocks which would 
feel like pins and needles running into you. 

Perhaps most of you have taken hold of 
the handles of a medical battery and have 
had shocks therefrom. In so doing, you have 
simply had the current from the secondary 
of an induction-coil. The current may be 
made weaker by sliding a metallic cover over 
part of the iron core and so shutting off part 
of the magnetic effect. 

SPARKING COILS 

While on this subject we may add that 
these coils will produce sparks from the two 
ends of the wire of the secondary coil. These 
sparks vary in length according to the amount 
of wire in the coil. Small ones are made 

43 



A-B-C OF ELECTRICITY 

which give a spark a quarter of an inch in 
length, while others are made which will give 
sparks 10, 12, and 16 inches in length. In 
the latter, however, there are many miles of 
wire in the secondary coil. 

The largest induction-coil known is one 
which was made for an English scientist. 
There are 341,850 turns, or 280 miles, of 
wire in the secondary coil. With 30 cells 
of Grove battery this coil will give a spark 
42 inches in length. You may form some 
idea of the effect of this induction-coil when 
we state that if we desired to produce the 
same length of spark direct from batteries, 
without using an induction-coil, we should 
require the combined volts of pressure of 
60,000 to 100,000 cells of battery. 

Having explained to you briefly the in- 
duction-coil — how it is made and its action — 
we must ask you to bear these principles in 
mind, and presently we will tell you how it 
is used in the telephone. 

The next thing we shall try to explain 
will be 

THE VIBRATING DIAPHRAGM 

Did you ever take the end of a cane in 

your hand, raise it up over your head, and 

then bring it down suddenly and sharply, so 
44 



THE TELEPHONE 



that it nearly touched the ground, as though 
you were about to strike something? If not, 
try it now with a thin walking-cane or with 
a pine stick about three feet long and one- 
half inch thick, and you will find that there 
is a peculiar sound given out. It is not the 
stick that makes this sound, but it is owing 
to the fact that you have caused the air to 
vibrate, or tremble, and thus give out a 
sound. 

If you strike a tuning-fork sharply you 
will see the ends vibrate and 
a sound will be given. If you 
put your fingers on top of a 
silk hat and speak near it you 
will feel vibrations of your 
voice. 

Every time you speak you 
cause vibrations of the air; 
and the louder and higher you 
speak the greater the number 
of vibrations. 

Suppose you take a thin 
piece of wood in your hands 
(say, for instance, the lid of a 
cigar-box cut in the shape shown in the pic- 
ture, Fig. 10) and hold it about two inches from 
your mouth and then speak. You will feel the 
wood tremble in your hand. This is because 

45 




Fig. 10 



A-B-C OF ELECTRICITY 



the vibrations of the air cause the wood to 
vibrate in the same manner. These vibra- 
tions are very minute and cannot be seen 
with the naked eye, but they actually take 
place, and could be measured with a deli- 
cately balanced instrument. 

Now let us try another experiment in 
further illustration of this principle. We 
will take a tube about three inches long and 
one and one-half or two inches in diameter. 
This tube may be made of cardboard. Now 
cut out a piece of thin cardboard which will 

just fit over one end 
of the tube. This 
piece we will call 
the " diaphragm." 
Fasten the dia- 
phragm by pasting 
it with two strips of 
thin paper to the 
tube. These strips 
of paper should be 
fastened only on the 
ends, and the middle of the paper allowed to 
be slack, as shown in the picture, so that the 
diaphragm may work backward and forward 
easily. Take a small shot about the size 
seen in the sketch and tie it to a single thread 
of fine silk, then let it hang as shown in the 

46 




Fig. 11 



THE TELEPHONE 

sketch (Fig. 11), so that it will only just touch 
the diaphragm. Now, if you speak into the 
open end of the tube the diaphragm will vi- 
brate and the shot will be seen to move to and 
from it according to the strength of the vibra- 
tions. If we could by any means make a dia- 
phragm in another tube reproduce these same 
vibrations, we should hear the same words 
respoken, if the tube were held to the ear. 

While the vibrations caused by the human 
voice are too minute to be seen, it may seem 




Fig. 12 



surprising that they can be made to produce 
power. This is done by an ingenious mech- 
anism called a Phonomotor, perfected by 

47 



A-B-C OF ELECTRICITY 

the great inventor Thomas A. Edison, of 
whom every one has probably heard. This 
mechanism, when spoken or sung at (or into) 
immediately responds by causing a wheel to 
revolve. No amount of blowing will start 
the wheel, but it can instantly be set in mo- 
tion by the vibrations caused by sound. 

The Phonomotor (which is shown in the 
engraving (Fig. 12) has a diaphragm and 
mouthpiece. A spring, which is secured to 
the bedpiece, rests on a piece of rubber tubing 
placed against the diaphragm. This spring 
carries a pawl that acts on a ratchet or 
roughened wheel on the fly-wheel shaft. A 
sound made in the mouthpiece creates vibra- 
tions in the diaphragm; the vibrations of 
the diaphragm move the spring and pawl 
with the same impulses, and as the pawl thus 
moves back and forth on the ratchet-wheel 
it is made to revolve. 

The instrument, therefore, is of great 
value for measuring the mechanical force of 
sound waves, or vibrations, produced by the 
human voice. 

THE TRANSMITTER 

That part of the telephone into which we 
speak is called the transmitter. This is usu- 

48 



THE TELEPHONE 

ally a piece of hard rubber having a round 
mouthpiece cut through it. At the other 
side of this mouthpiece is placed a diaphragm 
made of a thin piece of metal, which is held 
in place by a light spring. Behind this dia- 
phragm, and very close to it, is placed a car- 
bon button. Between this carbon button 
and the diaphragm is a small piece of plati- 
num, which is placed so as to touch both 
the button and diaphragm very lightly. 
This platinum contact piece is connected 
with one of the wires running to the primary 
of the induction-coil, and the spring attached 



TO •RECEIVED OF THE 




Fig. 13 



to the carbon button is connected with the 
battery to which the other wire of the pri- 
mary is connected. This is all shown in the 
sketch of a transmitter. (Fig. 13.) 

A is the mouthpiece; B, the diaphragm; 
C, the carbon button; D, the wire at the 

4 49 



A-B-C OF ELECTRICITY 

end of which is the platinum contact; E, 
the battery; and F, the induction-coil; P, P 
are the wires to the primary, and S, S to 
the secondary wires. 

We will now say a few words about the 
receiver, and then describe the manner in 
which the telephone works. 



THE RECEIVER 

This is that part of the telephone which 
is held to the ear, and by which we can hear 
the words spoken into the transmitter of the 
telephone at the other end of the line. 

The receiver is made of hard rubber, and 
contains a permanent bar magnet, which is 




Fig. 14 

wound with wire so as to make it also an 

electromagnet when desired. In front of 

this magnet is placed loosely a diaphragm 

of thin sheet iron. This diaphragm is placed 

so as to be within the influence of the mag- 
50 



THE TELEPHONE 

net, but just so that neither one can touch 
the other. 

Fig. 14 is a sketch of the receiver. A 
and B are the wires leading to the magnet, 
C, and D is the diaphragm. E and F are 
where the wires connect, one from the secon- 
dary of the induction-coil in the other tele- 
phone, and the other connected with the earth. 

THE CARBON BUTTON 

The little carbon button plays an impor- 
tant part in the telephone. You will see from 
the sketch of the transmitter that the cur- 
rent of electricity will flow through the car- 
bon button to the contact point and through 
the wire to the primary of the induction- 
coil. 

Now, carbon has a peculiarity, which is 
this, that if we press this carbon button, ever 
so slightly, against the platinum contact, 
there would be less resistance to the flow of 
the electricity through the wire to the pri- 
mary, and the more we press it the less the 
resistance becomes. The consequence of this 
would be that more current would go to the 
primary, and the secondary would become 
correspondingly stronger. If the carbon 

button were left untouched, and nothing 
51 



A-B-C OF ELECTRICITY 

pressed against it, the flow of current through 
it -would be perfectly even. 

Having examined the inside of the trans- 
mitter and receiver, and understanding the 
effect of pressure on the carbon button, let 
us now see 



HOW THE TELEPHONE WORKS 

When we speak into the mouthpiece of the 
transmitter, the vibrations of the air cause 
the diaphragm to vibrate very rapidly, and, 
of course, every movement of the diaphragm 
presses more or less against the carbon but- 
ton, in consequence of which the currents 
passing through the primary of the induction- 
coil are constantly increased or diminished 
and thus produce similar effects, but mag- 
nified, in the secondary. 

The effect of this is that the magnet in the 
receiver of the other telephone is receiving 
a rapidly changing current, which, producing 
corresponding magnetic changes, makes the 
magnet alternately weaker or stronger. 
This influences, by magnetism, the iron dia- 
phragm accordingly, and makes it reproduce 
the same vibrations that were caused by the 
speech at the transmitter of the sending tele- 
phone. Thus, the same vibrations being 

52 



THE TELEPHONE 

reproduced, the original sounds are given out, 
and we can hear what the person at the send- 
ing telephone is saying. 

The action of the telephone illustrates well 
the wonderfully quick action of the electric 
current by the reproduction of these sound 
waves, or air vibrations, for they number 
many thousands in one minute's speech. 



VII 

ELECTRIC LIGHT 

WE have now arrived at a very interest- 
ing part of the study of electricity, as 
well as a more difficult part than we have 
yet told you of, but one which you can easily 
understand if you read carefully. 

You must all have seen electric lights, 
either in the streets or in some large buildings, 
for so many electric lights are now used 
that there are very few people who have not 
seen them. But perhaps some of you have 
only seen the large, dazzling lights that are 
used in the streets, and do not know that 
there is another kind of electric light which 
is in a globe about the size and shape of a 
large pear, and gives about the same light 
as a good gas-jet. 

These two kinds of electric lights have 
different names. 

The large, dazzling lights which you see 

in the streets are called " arc-lights," and the 
54 



ELECTRIC LIGHT 



#ET 



small, pear-shaped lamps, which give a soft, 
steady light, are called " incandescent lights. " 
We will tell you later why these names are 
given to them. 

The incandescent lights are generally used 
in houses, stores, theaters, 
factories, steamboats, and 
other places where a number 
of small lights are more pleas- 
ant to the eyes. The arc- 
lights (Fig. 15) are used to 
light streets and large spaces 
where a great quantity of light 
is wanted. 

It would not be pleasant to 
have one of these dazzling arc- 
lamps in your parlor — al- 
though it would give a great 
deal of light — because your 
eyes would soon become tired. 
But two or three of the small 
incandescent lights (Fig. 16) 
would be very agreeable, be- 
cause they would give you a 
nice, soft light to read or work 
by, and would not tire your 
eyes. So, you see, these two different kinds 
of lamps are very useful in their proper 
places. 

55 




Fig. 15 



A-B-C OF ELECTRICITY 



Now, if you will read patiently and care- 
fully, we will try and explain how both these 
lights are made. 
You have seen that the telegraph, tele- 
phone, electric bells, 
etc., are worked by 
batteries. Electric 
lights, however, re- 
quire such a large 
amount of current that 
it is too expensive to 
produce them in large 
quantities by batteries. 
A small number of 
lamps could be lighted 
by batteries, but if we 
were to attempt to use 
them to light 500 or 
1,000 lamps together, 
the expense would be 
so enormous as to 
make it entirely out of 
the question. 

There are many mill- 
ions of incandescent 
lamps in use in the United States, but you 
will easily see that there could not be that 
number used if we had to depend on batteries 

to light them. You will understand this 
56 




Fig. 16 



ELECTRIC LIGHT 



more thoroughly when you have finished 
reading this little book. 

Well, you will ask, if we cannot use bat- 
teries, what is used to produce these electric 
lights? 

Machines called " dynamo-electric ma- 
chines," or " generators," which are driven by 
steam-engines or water-power, are used to 
produce the electricity which makes these 
lamps give us light. 

You will remember that in the chapter 
on Magnetism we ex- 
plained to you how 
electricity makes mag- 
netism, and now we 
will explain how, in the 
dynamo, magnetism 
makes electricity. 

It has been found 
that the influence of a 
magnet is very strong 
at its poles, and that 
this influence is always 
in the same lines. This 
influence has been de- 
scribed as " lines of 
force," which you will 
see represented in the sketch above by the 

dotted lines (Fig. 17). Of course, these lines 
57 




A-B-C OF ELECTRICITY 

of force are only imaginary and cannot be 
seen in any magnet, but they are always 
present. The meaning of this term " lines of 
force, " then, is used to designate the strength 
of the magnet. 

Many years ago the great scientist Fara- 
day made the discovery that, by passing a 
closed loop of wire through the magnetic 
lines of force existing between the poles of a 
magnet, the magnetism produced the pecul- 
iar effect of creating a current of electricity 
in the wire. If the closed loop of wire were 
passed down, say from U to D, the current 
flowed in the wire in one direction, and if it 
were passed upward, from D to U, the cur- 
rent flowed in the other direction. Thus, 
you see, magnetism produces electricity in 
the closed loop of wire as it cuts through the 
magnetic lines of force. Just why or how, 
nobody knows; we only know that electricity 
is produced in that way, and to-day we make 
practical use of this method of producing it 
by embodying this principle in dynamo- 
machines, as we will shortly explain. 

In carrying this discovery into practice in 
making dynamo-machines we use copper 
wire. If iron were used, there would be a 
current of electricity generated, but it would 

be much less in quantity, because iron wire 

58 



ELECTRIC LIGHT 

has much greater resistance to the passage 
of electricity than the same size of copper 
wire. 

Perhaps you can understand it more thor- 
oughly if we state that when a closed loop 
of w r ire is passed up and down between the 
poles of a strong magnet there is a very per- 
ceptible opposition felt to the passage of the 
wire to and fro. 

This is due to the influence of the mag- 
netism upon the current produced in the 
wire as it cuts through the lines of force, and, 
inasmuch as these lines of force are always 
present at the poles of a magnet, you will 
see that, no matter how many times you 
pass the loop of wire up and down, there 
will be created in it a current of electricity 
by its passage through the lines of force. 




Fig. 18 

Suppose that, instead of using one single 
loop of copper wire, you wound upon a spool 
a long piece of wire like that in Fig. 18, and 
that you turned this spool around rapidly 
between the poles of the magnet, you would 

59 



A-B-C OF ELECTRICITY 

thus be cutting the lines of force by the same 
wire a great many times, and every time one 
length of the wire cut through the lines of 
force some electricity would be generated in 
it, and this would continue as long as the 
spool was revolved. But, as each length 
would only be a part of the one piece of wire, 
you will easily see that there would be a 
great deal of electricity generated in the 
whole piece of wire. 

All we have to do, then, is to collect this 
electricity from the two ends of the wire, 
and use it. If we should attach two wires 
to the two ends of this wire on the spool, they 




Fig. 19 

would be broken off when it turned around, 
so we must use some other method. We fix 
on the end of the spool (which is called an 
" armature") two pieces of copper, so that 
they will not touch each other (as in Fig. 19), 
and fasten the ends of the wire to these 
pieces of copper. This is called a " commu- 
tator, " and, as you see, is really the ends of 
the wire on the spool. Now we get two thin, 

60 



ELECTRIC LIGHT 

flat pieces of copper and fix them so that 
they will rest upon the copper bars of the 
commutator, but will not go round with it. 
These two flat pieces of copper are called 
the " brushes/ ' and they will collect from 
the commutator the electricity which is 
gathered in the wire around the spool. As 
the brushes stand still, two wires can be 
fastened to them, and thus the amperes of 
current of electricity, acted upon by the 
volts pressure, can be carried away to be 
used in the lamps, for you must remember 
that as long as the spool turns around it 
gathers more electricity while there is any 
magnetism for the wire on the spool to pass 
through. The constant revolving of the 
spool creates so much electricity that it is 
driven out from the wire on the spool, through 
the commutator to the brushes, and there it 
finds a path to travel away from the pressure 
of the new electricity which is all the time 
being made. 

In this way we get a continuous current 
of electricity in the two wires leading from 
the commutator, and can use it to light 
electric lamps or for other useful purposes. 

In explaining this to you, so far, we have 
used as an illustration of the magnet one of 
the steel permanent magnets in order to 

Gl 



A-B-C OF ELECTRICITY 

make the explanation more simple, but now 
that you understand how the electricity is 
made, we must explain to you something 
about the magnets that are used in dynamo- 
machines. We can perhaps make this more 
clear by giving another example. 

Suppose you had a dynamo which was 
lighting up 100 of the incandescent lamps, 
each of 200 ohms resistance and each requir- 
ing 100 volts pressure. Now each lamp 
would take just a certain quantity of elec- 
tricity, say half an ampere; so, the 100 
lamps would require one hundred times that 
quantity. But, if you turned off 50 of these 
lamps at once, the tendency would be for 
the pressure to rise above the 100 volts re- 
quired for the other 50, and they would be 
apt to burn out quicker. It is plainly to be 
seen, then, that we must have some means 
of regulating the magnetism so as to regulate 
the lines of force for the wire on the armature 
to cut through. We can do this with an 
electromagnet, but not with a permanent 
magnet, because we cannot easily regulate the 
amount of magnetism which a permanent mag- 
net will give. 

There is another reason why we cannot 
use permanent magnets in a dynamo, and 
that is because they cannot be made to give 

62 



ELECTRIC LIGHT 

as much magnetism as an electromagnet mill 
give. 

Thus you will see that there are very good 
reasons for using electromagnets in making 
dynamo-machines. Let us see now how these 
electromagnets and dynamos are made, and 
then examine the methods which are followed 
to operate and use them. 

You must remember, to begin with, that 
in referring to wire used on magnets and 
armatures and for carrying the electricity 
away to the lamps, we always mean wire 
that is covered or insulated. In electric light- 
ing, insulated wire is always used, except at 
the points where it is connected with, the 
dynamo, the lamps, a switch, or any point 
where we make what is called a "connec- 
tion." 

As the shape of the magnets is different in 
the dynamos of various inventors, we will 
take for illustration the one that is nearest 
the shape of the horseshoe and the shape that 
is generally used in illustrating the principle 
of the dynamo. This is the form used by 
Mr. Edison, whom we have previously men- 
tioned. This form is shown in Fig. 20. 

Now, although this magnet appears to be 
in one piece, it really consists of five parts 
screwed together so as to make, practically, 

63 



A-B-C OF ELECTRICITY 



one piece. The names of the parts are as 
follows: F, F are the "cores"; C the "yoke," 
which binds them together ; and P, P the "pole 

pieces," where 
the magnetism 
is the strongest. 
These pole 
pieces are round- 
ed out to receive 
the armature, 
which, as you 
will remember, 
is the part that 
turns around. 

The cores, F,F, 
are first wound 
with a certain 




Fig. 20 



amount of wire, which depends upon the 
use the dynamo is to be made for. Thus, 
you will see, there will be on each core two 
loose ends of the wire that is wound around 
it — namely, the beginning of the wire and 
the end where we leave off winding, which 
on the two cores together will make four ends 
of wire. We will tell you presently what is 
done with them. 

After the cores are wound, they are screwed 
firmly to the yoke and to the pole pieces, so 
as to make, for all practical purposes, one 

64 



ELECTRIC LIGHT 

whole piece pretty nearly the shape of a 
horseshoe magnet. 

Now, to make the dynamo complete, we 
must put in the armature between the poles, 
which are rounded off, as you will see, to 
accommodate it. The armature is held up 




Fig. 21 

by two " bearings," which you will see in 
the sketch of the complete dynamo above. 
(Fig. 21.) 



A-B-C OF ELECTRICITY 

The armature in a practical dynamo-ma- 
chine consists of a large spool made of thin 
sheets of iron firmly fastened together and 
having a steel shaft run through the center, 
upon which it revolves. 

This spool, or armature, is wound with a 
number of strands of copper wire. The com- 
mutator, instead of consisting of two bars, 
is made in many dynamos with as many bars 
as there are strands of wire, and the ends of 
these wires are fastened to the bars of the 
commutator so as to make, practically, one 
long piece of wire, just as we showed you in 
explaining how the electricity was produced. 

The brushes, resting upon the commutator, 
carry away the electricity from it into the 
wires with which they are connected. 

Now we have our dynamo all put together 
and ready to start as soon as we properly 
connect these four loose ends of wire on the 
cores. 

If you will turn back to Fig. 20 you will 
see that two of the wires are marked I, and 
the other two O. The letter I means the 
inside wire, or where the winding began, and 
the letter O means the outside wire, or where 
we left off winding. 

Now, if we fasten together (or " connect") 
the two ends of wires, I and O, near the top 

66 



ELECTRIC LIGHT 

of the magnet, we make the two wires round 
the cores into one wire, which starts, say, at 
I near the poles, goes all around one core, 
crosses over and around the other core down 
to the other end of the wire to O, near the 
poles. 

So far we have called the iron a magnet, 
although it is not a magnet until electricity 
is put into it; so, when the dynamo is started 
for the first time, these two ends of wire, I 
and 0, are connected to a battery or other 
source of current for the purpose of sending 
electricity through the wire on the cores. 
When the electricity goes into this wire the 
iron immediately becomes a magnet, and the 
lines of force are present at the poles. 

Now, the armature is turned around rapid- 
ly by a steam-engine, and, as the wire on the 
armature cuts the lines of force with great 
rapidity and so frequently, there is quickly 
generated a large quantity of electricity, 
• which passes out as fast as it is made through 
the commutator and the brushes to the lamp. 
And so long as the armature is revolved and 
the battery attached, the electricity will be 
made, or, as it is usually termed, "generated." 

As we stated above, a battery is used the 

first time the dynamo is run, and now we will 

explain why it is not needed afterward. 
67 



A-B-C OF ELECTRICITY 

Although iron will not become a perma- 
nent magnet, like steel, it does not lose all its 
magnetism after it has been once thoroughly 
charged. When the dynamo is stopped, 
after the first trial, and the battery is taken 
away, you will discover only traces of mag- 
netism about the poles. They will not readily 
attract even a needle or iron filings; but 
there is, nevertheless, a very small amount 
of magnetism left in the iron. Small as this 
magnetism is, however, it is enough to make 
very faint and weak lines of force at the 
poles of the magnet. 

After the battery is taken away, the ends 
of the wire on the cores, which were connected 
to the battery, are connected, instead, to the 
wires which carry away the electricity from 
the brushes to the lamps. Thus, you will 
see, if any electricity goes from the dynamo 
to the lamps, part of it must also find its way 
through the wires which are around the 
cores. 

We will now start up the dynamo without 
having any battery attached and see what 
happens. The armature turns around and 
the wires upon it cut through those very faint 
lines of force which are always at the poles. 
This, as you know, makes some electricity; 
very little, to be sure, but it comes out 

68 



ELECTRIC LIGHT 

through the brushes to the wires leading to 
the lamps, and there it finds the wires lead- 
ing back to the cores. Well, part of this 
weak current of electricity goes into these 
wires and travels back round the cores and 
so makes the magnetism stronger. The con- 
sequence of this is that the lines of force be- 
come stronger and, as the armature keeps 
turning around, the electricity naturally be- 
comes stronger, and so there is more of it 
going through the wires back to the cores 
and increasing the strength of the magnet all 
the time, until the dynamo becomes strong 
enough to generate all the current it was in- 
tended to give for the lamps. 

Of course, you understand that the strong- 
er the magnet becomes, the greater will be 
the lines of force and the greater the amount 
of electricity made by the turning of the 
armature. Now, there is naturally a limit 
to what can be done with any particular 
dynamo; so, while the electricity continues 
to strengthen the magnetism and the mag- 
netism increases the electricity, this cannot 
go beyond what is called the " saturation' 9 
point of the magnet. 

Saturation means that the iron is full of 
magnetism, and will hold that much but no 
more. You will learn more as to the satura- 

69 



A-B-C OF ELECTRICITY 

tion of magnets when you study electricity 
more deeply, and we therefore do not intend 
to enter into that subject in this book. We 
will only state, however, that the magnets of 
dynamos are not always charged up to their 
saturation point. , 

THE LAMPS 

So far you have learned how the current 
of electricity is produced, and now we will 
follow along the wires to find out how it 
makes the lamps give out both strong lights 
and the smaller, pleasant ones. 

Suppose we take first the large, dazzling 
lights we see in the streets, which, as you 
know, are called 

ARC-LIGHTS 

Those who have seen the arc-lamps will 
readily recognize them from the picture in 
Fig. 22. 

You will see that there are two sticks, or 
"pencils," of carbon. Now you will remem- 
ber that in the chapter on Magnetism we 
told you that in order to have electricity do 
work for us we must put some resistance or 

opposition in its way. When we get light 
70 



ELECTRIC LIGHT 



from an electric lamp it is because we make 
the electricity do some work in the lamp, 
and this work is in pushing its way through 
a resistance or opposition 
which is in the lamp. 

When we generate electric- 
ity in the dynamo and put 
two wires for it to travel in, 
the current goes away from 
the dynamo through one of the 
wires and will go back to the 
dynamo through the other 
one if it can possibly get a 
chance to get to this other 
one. Now, the electricity 
which is constantly being 
made fills the wires and acts 
as a pressure to force the cur- 
rent through the wires back to 
the dynamo, and, if we put no 
resistance or opposition in the 
way, it would have a very easy 
path to travel in and would do 
no work at all. The wires 
leading to an electric lamp should have very 
little resistance, not sufficient to require any 
work from the current in passing through. 

So, if we bring the two carbons in an arc- 
lamp together they really form part of the 
71 



Fig. 22 



A-B-C OF ELECTRICITY 

wire, and do not interrupt the current in its 
travels, but, if we separate the carbons, we 
make a gap which the current must jump 
across if it wants to go on. As the volts, or 
pressure, is so great, the current must jump, 
and this against the resistance or opposition 
in an arc-lamp is that which gives the cur- 
rent so much work to do. Indeed, so hard 
is it for the current to jump across this gap 
that it breaks off from one carbon a shower 
of tiny particles as fine as the finest dust, and 
makes them white hot in passing to the other. 
This shower of fine carbon dust, together with 
the ends of the carbons, being white hot, of 
course makes a light, and this is the dazzling 
light which you see in the arc-lamp. 

Of course, when the electricity has jumped 
over from one carbon to the other, it goes 
through it to the wire, and so passes on to 
the next lamp, where it has to jump again, 
and so on until it has gone through the last 
lamp, then it has an easy path to get back 
to the dynamo. 

Now, we want you to understand more 
thoroughly how that much resistance or op- 
position will cause heat, so we will try to give 
you a simple, , example. 

Most of you know that if you were hold- 
ing a rope tightly in your hands and some 
72 



ELECTRIC LIGHT 

one pulled it through them quickly and sud- 
denly, it would get very hot and your hands 
would feel as though they were being burned. 
This is heat caused by your hands resisting 
or opposing the passage of the rope through 
them, and if you could hold on tightly enough 
and the rope was drawn through quickly 
enough, it would take fire. This fire would, 
therefore, cause heat and light. 

It is just this principle of resistance to the 
passage of the current which causes the light 
in an arc-lamp, as we have shown you. 

INCANDESCENT LAMPS 

You have just learned that the light in an 
arc-lamp is caused by the current forcing off 
from the carbon sticks tiny particles and 
heating them up until they give a brilliant 
light. So, you see, in an arc-light there is 
a wearing away of carbon by electricity, and 
therefore these sticks, or pencils, of carbon 
in time are all burned away. In practice 
the carbon pencils last about eight or ten 
hours, and then new ones must be put in. 

Now, in the incandescent lamp there is 
also carbon used, but the light is not pro- 
duced by the combustion or wasting away 

of the carbon, as we will show you. 
73 



A-B-C OF ELECTRICITY 



The picture below will show you 
the appearance of an incandescent lamp. 
(Fig. 23.) 
You will see that this lamp consists of a 
pear-shaped globe, 
and inside is a long 
U-shaped strip of 
carbon no thicker 
than an ordinary 
thread. This is a strip 
of bamboo cane 1 which 
has been carbonized to 
a thread of charcoal. 
It is joined to two wires 
which come through 
the glass. These two 
wires come down 
through the bottom of 
the globe, and one is 
fastened to a brass 
screw -ring, while the 
other wire is fastened 
to a brass button at 
the bottom of the 
lamp. These two (the 
ring and button) must, as you know, be sep- 
arated from each other by something which 

ir The filaments in modern "Mazda" lamps, as made at 
the Edison Lamp Works, are strips of metallic tungsten. 
74 




Fig. 23 



ELECTRIC LIGHT 



will not carry electricity, or they would make 
a short circuit when the electricity was ap- 
plied. We separate the ring and the button 
in various ways. 

Now, if we took the ends of two wires 
which were charged with the proper amount 
of electricity and put 
one wire on the screw- 
ring and the other on 
the button, the lamp 
would light up, because 
there would be a com- 
plete path for the cur- 
rent to travel in. 

It will, however, be 
plain to you that it 
would be awkward to 
light the lamps in this way, so we use a 
"socket" into which the lamp is screwed. 
(Fig. 24.) 

The wires from the dynamo carrying the 
electricity are connected in the socket, one wire 
with the screw thread into which the screw- 
ring fits, and the other with a button which 
the button on the lamp touches when the 
lamp is screwed into the socket. Thus we 
have a connected path for the current to 
travel in, or, as it is termed, a complete cir- 
cuit. 

75 




Fig. 24 



A-B-C OF ELECTRICITY 

You will notice that in the incandescent 
lamp the electricity does not need to jump, 
as it does in the arc-light, because we give 
it one continuous line to travel in. 

In order, however, to get the current to 
do work for us, we put some resistance in its 
path, which it must overcome in order to 
travel back to the dynamo. The resistance 
in an incandescent lamp is the U-shaped car- 
bon strip (or, as it is called, "filament"). 
This charcoal filament has so much greater 
resistance than the wires that it opposes, or 
resists, the passage of the electricity through 
it; but the electricity must go through, and, 
as it is strong enough to force its way, it 
overcomes this resistance and passes on 
through the carbon to the wire at the other 
end. You see it is a struggle between the 
carbon and the electricity, the current being 
determined to go on and the carbon trying 
to keep it back; and, in the end, the elec- 
tricity, being the stronger, gets the best of 
it; but the struggle has been so hard that 
the carbon has been raised to a white heat, 
or incandescence, and so gives out a beautiful 
light, which continues as long as the current 
of electricity flows. 

You will remember that in the arc-light the 

carbons are slowly consumed and new ones 
76 



ELECTRIC LIGHT 

must be put in. If the carbon in the in- 
candescent light were consumed, it would not 
last many minutes, because it is only about 
the size of a horsehair. Now, you will natu- 
rally inquire why this fine strip is not burned 
up when it is raised to so high a heat. Well, 
we will tell you. 

You know that if you light a match and 
let it burn the wood will all be consumed. 
But did you ever light a match, put it into 
a small bottle, and put the cork in? If you 
never did, do so now as an experiment, and 
you will see that the match will keep lighted 
for an instant and then go out without con- 
suming the wood. 

The reasons for this are very simple. In 
order to burn anything up entirely it is ab- 
solutely necessary to have the gas called 
oxygen present, and, as the air you live in 
contains a very large amount of oxygen, 
there is more than sufficient in your room 
to cause the wood of the match to be entirely 
consumed after it is lighted. But there is 
such a small quantity of oxygen in the bottle 
that it is not enough to keep the fire going 
in the match, and, consequently, it will not 
burn up the wood. 

The reason the filament in an incandes- 
cent lamp is not burned up is because there 

77 



A-B-C OF ELECTRICITY 

is no oxygen inside the globe. After the 
carbon is put in its place all the oxygen is 
drawn out through a tube, and the glass is 
sealed up so that no more oxygen can get in. 
This is called obtaining a "vacuum," and 
vacuum means a space without air. 

There being no oxygen in the globe, it is 
impossible for the carbon to burn up; so 
the incandescent lamp will continue to give 
its light for a very long time, some of them 
lasting for thousands of hours. Some day, 
however, from a great variety of obscure 
causes, the filament becomes weak in some 
particular spot and breaks, and the light 
ceases. When this happens, we unscrew the 
lamp and put another one in, and the light 
goes on as usual. 

Now you have learned how the incandes- 
cent lamp is made to give light. We will add 
that it is a beautiful, soft, white light, almost 
without heat, it will not explode, throws off 
no poisonous fumes like gas or oil lamps, and 
has many other points of comfort and con- 
venience which make it very desirable. 

ELECTRIC-LIGHT WIRES 

Before closing the subject of electric light 
you would perhaps like to know something 

78 



ELECTRIC LIGHT 



about the way in which we 
leading to the lamps. 

If you remember what we 
measurements in the be- 
ginning of this book, it will 
be easy to understand what 
follows : 

You know that if you 
have a very great pressure 
you can force a quantity 
through a small conductor. 
This is the principle upon 
which the arc - lamps are 
run. Every arc-lamp takes 
about 40 to 50 volts and 
from 5 to 10 amperes to 
produce the light, and they 
are connected with the wires 
as shown in Fig. 25. 

This is called running 
lamps in "series," and, as 
you will see from the sketch, 
the wire starts out from the 
dynamo and connects with 
one carbon of the first arc- 
lamp, and to the other car- 
bon is connected another 
wire which goes on to the 
next lamp, and so on until 

79 



place the wires 
told you about 



LAM? 



Fig. 25 



A-B-C OF ELECTRICITY 

the last lamp is reached, and then the wire 
goes back to the dynamo. This forms, prac- 
tically, one continuous loop from one brush 
to the other of the dynamo. 

The current starts out, makes its way 
through the first lamp, goes on to the next, 
makes its way through that, and so on till 
it has jumped the last one; then it goes back 
to the dynamo. 

Now, as each of these jumps requires a 
pressure of 40 or 50 volts, you will easily see 
that the total pressure, in volts, of the elec- 
tricity must be as many times 40 or 50 volts 
as there are lamps to be lighted; so, if there 
were 60 lamps in circuit, there would be 
2,400 to 3,000 volts pressure, which, while 
it gives very fine lights, might cause instant 
death to any one touching the wires. 

Suppose anything happened to the first 
lamp, which stopped the current from jump- 
ing through it. There would be no path for 
the current to travel farther, and, conse- 
quently, all the lights would go out. To get 
over this difficulty there is sometimes used 
what is called a "shunt," which only acts 
when the lamp will not light. This shunt 
carries the current round the lamp to the 
other wire, so that it may travel on and light 

up the other lamps. 

80 



ELECTRIC LIGHT 



WIRES FOR INCANDESCENT LAMPS 



for 



an 



The wiring 
carried out in 
ly different way, which 
you can see by compar- 
ing Fig. 25 A with Fig. 25 
which shows the wiring for 
arc-lamps. 

This is called connecting 
in " multiple arc." 

You will notice that the 
two wires running out from 
the dynamo (which are 
called the main wires) do 
not form one continuous 
loop as in the arc-light sys- 
tem, but that a smaller wire 
is attached to one of the 
main wires and then con- 
nected with the screw-ring 
in the lamp-socket; then an- 
other wire is connected with 
the button in the socket and 
afterward to the other main 
wire. Every lamp forms an 
independent path through 
which the current can travel 
back to the dynamo. 

6 81 



incandescent lamps 
entire- 



is 





1>" 

LAMP 
LAMP 






'I" 

LAMP 

IT 

LAMP 






LAMP 






LAMP 




DYNAMO 



Fig. 25 A 



A-B-C OF ELECTRICITY 

Now, if we turn one of these incandescent 
lamps out, we simply shut off one of these 
paths and the electricity travels through the 
other lamps, and, if we wish, we can turn 
out all the lamps but one and there will still 
be a way for the electricity to go back to 
the dynamo. 

In the arc-lamps we must have a very high 
number of volts pressure, because the elec- 
tricity has only one path, and it all has to 
pass through the first and other lamps till 
it comes to the last one. In the incandes- 
cent light the electricity has as many paths 
as there are lamps, so we only need to keep 
one certain pressure in volts in the main wires 
all the time. This pressure is even all the 
way through the main wires, and, therefore, 
it is ready to light a lamp the instant it is 
turned on, because, as you have seen, elec- 
tricity will always get back to the dynamo 
if there is a possible chance, and the lamp 
opens a path. 

The volts pressure used to operate any 
number of incandescent lamps is altogether 
very much less than for a number of arc- 
lights. For example, in the Edison system 
the pressure (sometimes called " electro- 
motive force ") is only about 110 volts, which 
is very mild and not at all dangerous. This 

82 



ELECTRIC LIGHT 

electromotive force would be the same if there 
were one lamp or ten thousand lighted. 

While this Edison current would not hurt 
any one, you should remember that it is 
much the better plan not to touch any elec- 
tric-light wires until you have learned a 
great deal more on this subject. 

We may add that each of the standard 
incandescent lamps requires only about one- 
quarter of an ampere of current to make 
them give a light of 16 candle-power, which 
is about the light given by a very good 
gas-jet, and while the electromotive force, 
or pressure, would only be about 110 volts, 
whether there were one lamp or ten thousand 
lighted, there must be sufficient amperes in 
the wires to give each lamp its proper 
quantity. 

SWITCHES 

We have made mention several times of 
turning on or off one or more lights, and now, 
perhaps, you would like to know how this 
is done. 

Suppose the electricity was traveling 
through wires to one or several lamps, it 
would light up those lamps as long as the 
wires provided a path to travel in, but if you 
were to cut out one of them, which is called 

83 



A-B-C OF ELECTRICITY 

" breaking the circuit/' there would be no 
road for the electricity to follow, and, conse- 
quently, its course would be stopped short 
and the lamps would go out. You will re- 
member that electricity must have a complete 
circuit or it can do no work, and in electric 
lighting it is always a metallic circuit that 
is used. 

Now, the switch is simply a device which 
is used to break the circuit so that the cur- 



jCIRCl/IT 



BROKEN 




WIR.E 



CIRCUIT 




CLOSED 



rent cannot pass on. The simplest form of 
switch is seen in the sketch. (Fig. 26.) 

You will see that there is a wire cut in two, 
and to one piece is attached a metallic piece, 
A, which turns one way or the other, and 
when it is turned so as to touch the other 
part of the wire the circuit is closed and the 
electricity goes from the lower part of the 
wire through the metallic piece A to the 
other part of the wire, thus making a com- 

84 



ELECTRIC LIGHT 

plete circuit or path for the electricity to 
travel in. 

If we turn the piece A away from the upper 
wire this breaks the circuit and cuts off the 
path, and, of course, the lamps would go out. 

This is the principle of the switch, and, 
although they are made in thousands of ways, 
switches all have the same object — namely, 
the closing and breaking of the circuit, 
whether it is for one or .a hundred lamps. 

WIRE ON DYNAMOS 

In explaining to you the construction and 
working of dynamo-machines, we did not 
state anything about the amounts of wire 
used in winding the machine. 

It is not our intention to say exactly how 
much is used on any one dynamo, because 
that is among the things you will have to 
learn when you come to study the subject 
of electricity more deeply. 

We simply want to have you understand 
that upon the number of turns of wire on 
any one machine depends the effect that 
that amount of wire, carrying electricity, 
will have upon a certain weight of iron when 
the armature is revolved a certain number 
of turns per minute. 

85 



A-B-C OF ELECTRICITY 

A certain number of strands of wire on an 
armature will only do a certain amount of 
work at the most, so you will see that a 
small dynamo will not produce as much elec- 
tricity as a larger one containing more iron 
and wire. For high pressure there must be 
more strands of wire cutting the lines of force 
more frequently than would be required for 
low pressure; and, to produce a great many 
amperes, the armature must be larger and 
the wire upon it thicker than it would need 
to be if only a small number of amperes were 
wanted. 

This of itself is a very deep and compli- 
cated subject, and many books have been 
written upon it alone. We shall, therefore, 
not attempt to go more deeply into it in 
this little book, but simply content ourselves 
with giving you the general idea, which will 
be sufficient until you make a thorough 
study of the subject. 



VIII 

ELECTRIC POWER 

ONE of the most convenient uses to which 
electricity is put is in producing motive 
power for driving all kinds of machines, from 
a sewing-machine to a railway train, and we 
will now try to explain how we can get this 
kind of work from electricity. 

To begin with, you all know that a piece 
of machinery is usually made to work by 
revolving a wheel which is part of the ma- 
chine, either by means of a steam-engine or 
by water-power, or, as a sewing-machine, by 
foot-power. Now, when we work a piece of 
machinery by electricity we do just the same 
thing by using, instead of the steam-engine 
or water or foot power, an electric - engine 
called an " electromotor/' which operates in 
the same way — namely, by turning the wheel 
of the machine it is applied to. 

Foot -power is hard work for the person 
who is applying the power, and, as you can 

87- 



A-B-C OF ELECTRICITY 

easily see, one person can make only a very 
little power by use of the feet. Steam and 
water power can be used for any large amount 
of work, but the work must be within a few 
hundred feet of the engine or the power can- 
not be used. 

If there were a factory using steam-power 
a block or two away from where you lived, 
and you had a lathe in your house which 
you would like to have run by the steam- 
power in the factory, it would be practically 
impossible to do this. Now, if the factory 
were still farther away from your house, it 
would be still more impossible, and if it were 
a mile away it would be foolish to dream 
of taking steam-power from a place so far 
away. 

Suppose, however, that this factory was 
lighted by electric lights, it would be a very 
easy matter to take some of the power over 
to your house. This could be done, even if 
the factory were miles away, by taking two 
wires from their electric-light wires and run- 
ning them into your house to an electro- 
motor connected with your lathe. This 
electromotor would then run your lathe just 
as well as if it were belted to a steam-engine. 

So, you see, power can be carried in the 

form of electricity through two wires over 

88 



ELECTRIC POWER 

very great distances and made to do work 
at a long way from the engine which is turn- 
ing the dynamo to make the electricity. 
Thus, you may have brought into your house 
wires which will give lights and, at the same 
time, power to run a sewing-machine, a lathe, 
or any other piece of machinery. 

Having learned so far that a dynamo will 
make a continuous current of electricity, and 
that two wires will carry this current to any 
place where it is wanted, let us now see what 
takes place in the electromotor to transform 
the electricity into power. 

An electromotor (which we will now call 
by its short name, motor) is simply a ma- 
chine made like a dynamo. Curious as it 
may seem to you, it is a fact that if you take 
two dynamo-machines exactly alike, and run 
one with the steam-engine so as to produce 
electricity, and then take the two main 
wires and attach them to the brushes of the 
other dynamo, the electricity will drive this 
other dynamo so as to produce a great deal 
of power which could be used for driving 
other machines. Thus, the second dynamo 
would become a motor. 

In the chapter on dynamos we explained 
something about the way they were made 
and how the electricity was produced. 

89 



A-B-C OF ELECTRICITY 

THE MOTOR 

You will remember that the armature con- 
sists of a spool wound with wire. This spool 
is made of iron plates fastened together so 
as to form one solid piece. The armature of 
a motor may be made in the same way; in 
fact, the whole motor is practically a dynamo- 
machine. 

There is something more about magnetism 
which we will tell you of here, because you 
will more easily understand it in its relation 
to an electromotor. 

If we take an ordinary piece of iron and 
bring one end of it near to (but not touching) 
one pole of a magnet, this piece of iron will 
itself become a weaker magnet as long as it 
remains in this position. This is said to be 
magnetism by " induction." The end of the 
piece of iron nearest to the magnet will be of 
the opposite polarity. For instance, if the 
pole of the magnet were north, the end of 
the iron which was nearest to this north 
pole would be south, and, of course, the 
other end would be north. To make this 
more plain we show it in the following sketch. 
(Fig. 27.) 

This would be the same whether the mag- 
net were a permanent or an electromagnet. 

90 



ELECTRIC POWER 

You will remember also that the north 
pole of one magnet will attract the south pole 
of another magnet, but will repel a north 
pole. 

These are the principles made use of in an 




STEEL PERMANENT MAGNET IRON 

Fig. 27 

electromotor, and we will now try to show 
you how this is carried into practice. 

Although a motor is made like a dynamo, 
we will show a different form of machine 
from the dynamo already illustrated, because 

91 



A-B-C OF ELECTRICITY 




it will help you to understand more easily. 
(Fig. 28.) 

Here we have an electromagnet with its 
poles, and an iron armature wound with 

wire, just as in the 
dynamo we have de- 
scribed, except that 
its form is different. 
A commutator 
and brushes are also 
used, but the elec- 
tricity, instead of 
being taken away 
from the brushes, is 
taken to them by 
the wires connected 
with them. Two wires are also connected 
which take part of the electricity around 
the magnet, just as in the dynamo. 

Now, when the volts pressure and amperes 
of electricity coming from a dynamo or bat- 
tery are turned into the wires leading to the 
brushes of the motor, they go through the 
commutator into the armature and round 
the magnet, and so create the lines of force 
at the poles and magnetize the iron of the 
armature. 

Let us see what the effect of this is. 
The poles of the magnet become north and 

92 



Fig. 28 



ELECTRIC POWER 

south, and the four ends on the armature also 
become north and south, two of each. 

By referring to Fig. 28 again we shall see 
what takes place. 

The north pole of the magnet is doing two 
things: it is repelling, or forcing away, the 
upper north pole of the armature and at the 
same time drawing toward itself the lower 
south pole of the armature. 

In the mean time the south pole of the 
magnet is repelling the south pole of the 
armature and at the same time drawing tow- 
ard itself the north pole of the armature. 

This, of course, makes the armature turn 
around, and the same poles are again pre- 
sented to the magnet, when they are acted 
upon in the same manner, which makes the 
armature revolve again, and this action con- 
tinues as long as electricity is brought 
through the wires to the brushes. Thus, the 
armature turns around with great speed and 
strength, and will then drive a machine to 
which it is attached. 

The speed and strength of the motor are 
regulated by the amount of iron and wire 
upon it, and by the volts pressure and am- 
peres of electricity supplied to the brushes. 
Motors are made from a small size that will 
run a sewing-machine up to a size large 

93 



A-B-C OF ELECTRICITY 

enough to run a railway train, and are often 
operated through wires at a great distance 
from the place where the electricity is being 
made, sometimes miles away. 

They are also made in a great many dif- 
ferent forms, but the principle is practically 
the same as we have just described to you. 



IX 

BATTERIES 

SO far we have only described one way 
of producing electricity — namely, by 
means of a dynamo-machine driven by steam 
or water power. The supply of electricity 
so obtained is regular and constant as long 
as the steam or water power is applied to the 
dynamo. 

There is another and very different way 
of producing electricity, and this is by means 
of a chemical process in what is called a bat- 
tery. 

To obtain electricity from the dynamo we 
must spend money for the coal to make the 
steam which operates the steam-engine, or 
for the water which turns the water-wheel, 
as well as for an engineer in both cases. 
When we obtain electricity from a battery 
we must spend money for the chemicals and 
metals which are constantly consumed in 
the battery. 

95 



A-B-C OF ELECTRICITY 

PRIMARY BATTERIES 

An electrical battery is a device in which 
one or more chemical substances act upon a 
metal and a carbon, or upon two different 
metals, producing thereby a current of elec- 
tricity, which will continue as long as there 
is any action of the chemicals upon the metal 
and carbon, or upon the two metals. 

Batteries for producing electricity may be 
divided into two classes, called "open cir- 
cuit' \ batteries and "closed circuit" bat- 
teries. 

Open-circuit batteries are those which are 
used where the electricity is not required con- 
stantly without intermission — for instance, in 
telephones, electric bells, burglar alarms, gas- 
lighting, annunciators, etc. 

Closed-circuit batteries are those which 
are used where the effect produced must be 
continuous every moment, as, for instance, 
in electric lights and motors. 

The open-circuit battery is made in many 
different ways, so we only describe two of 
the principal ones. 

As we told you in an early part of this 
book, we do not know just what electricity 
is, nor why it is produced under the condi- 
tions existing in a battery. But we do know 



BATTERIES 

that by following certain processes and mak- 
ing certain chemical combinations we can 
make as much electricity and in such pro- 
portions as we want. 

The two metals, or the metal and carbon, 
in a battery are called the "elements," and 
to these are connected the wires which lead 
from the battery to the instruments to be 
worked by it. 

The Leclanche Battery. — This form of open- 
circuit battery consists of a glass jar in which 
is placed the elements. One element con- 
sists of a rod of zinc, and the other element 
is carbon and powdered black oxide of 
manganese. These two (the carbon and 
black oxide of manganese) are placed in an 
earthenware vessel called a "porous cup." 
This is simply a small jar made of clay 
which is not glazed. Thus, the liquid which 
is in the glass jar penetrates through the 
porous cup to the carbon and manganese 
which it contains, and so the chemicals affect 
both these and the zinc at once, for, in order 
to obtain electricity, you will remember that 
the chemical action must take place at the 
same time upon both the elements in the 
same vessel. (Fig. 29.) 

The chemical substance used in this bat- 
tery is sal-ammoniac, or salts of ammonia. 

7 97 



A-B-C OF ELECTRICITY 




A certain quantity of this salt is dissolved 
in water, and this solution is poured into the 
glass jar. When this is done the battery will 
generate electricity at once. 

It should be remembered that the proper 
term for the chemical 
mixture which acts upon 
the elements in any bat- 
tery is "electrolyte." 

The Dry Battery. — 
The cleanliness, conven- 
ience, high efficiency, 
and comparatively low 
internal resistance of the 
dry cell has brought it 
into great favor in the 
last few years. It is 
now extensively used in 
preference to the 
Leclanche and other 
open - circuit batteries 
having liquid electrolyte 
for light work, such as bells, gas-lighting, 
burglar alarms, ignition on motor -boats, 
automobiles, etc. 

The dry cell is also used in great numbers 
for pocket flash-lamps, and in other ways 
where it would be impossible to employ bat- 
teries containing liquids. 




Fig. 29 



BATTERIES 

A dry cell consists of zinc, carbon, and the 
electrolyte, which is a mixture so made that 
it is in the form of a gelatinous or semi- 
solid mass, so that it will not run or slop 
over. 

A piece of sheet zinc is formed into a long 
tube, and a round, flat piece of zinc is soldered 
at one end, thus making a cup open at one 
end. This forms the cell itself, and at the 
same time becomes one of the elements. 
The other element is a piece of battery car- 
bon which is long enough to project out of 
the top of the cell about half an inch or more. 
While the cell is being filled with the electro- 
lyte the carbon is held up by a support so 
that it does not touch the zinc at the bottom 
of the cup. Of course, the zinc cup and the 
carbon are provided with proper binding- 
posts or other attachments, so that conduct- 
ing wires can be connected. 

The electrolyte is packed into the cup and 
around the carbon in such a way that the 
cup is entirely filled within about half an 
inch from the top, and then some melted tar 
or pitch is poured over the top of the electro- 
lyte. This seals the cell and binds the con- 
tents solidly together. Just before the seal- 
ing compound hardens, one or two holes are 
made in it so that the gases may escape. 

99 



A-B-C OF ELECTRICITY 

The composition of the electrolyte itself 
is not exactly alike in all dry cells, as the 
various manufacturers follow their own par- 
ticular formulas. However, as you may be 
curious to know something about it, we 
would state that one formula embraces 
flour, water, plaster of Paris, granulated 
carbon, zinc chloride, ammonium chloride, 
and manganese binoxide. 

You will remember that the Leclanch6 and 
the dry batteries are purely open-circuit 
cells, and that they can be used to advantage 
for electric bells, annunciators, burglar 
alarms, gas ignition, etc., where the current 
of electricity is not doing continuous work, 
but only for a few seconds at a time. Conse- 
quently, the batteries have a little rest in 
between, if only for a few seconds. 

Now, if we were to attempt to use open- 
circuit batteries for electric lights or motors, 
where the electricity must work constantly 
every second, the batteries would "polarize" 
— that is to say, they would only work a few 
minutes and then stop, because the chemicals 
used in them are of that kind that they will 
only allow the battery to do a little work 
at a time. 

The batteries we have been describing will 

do the ordinary work for which they are in- 
100 



BATTERIES 

tended for sometimes a year without requir- 
ing any attention, but if we try to make them 
do work for which they were not intended, 
they would only last a few days. 

If we should want to operate electric lights 
or motors continuously from a battery we 
must, therefore, use 

CLOSED-CIRCUIT BATTERIES 

There is a great variety of ways in which 
closed-circuit batteries are made, but, as the 
main principles are very much alike, we will 
only describe two general kinds, those with 
and those without a porous cup. 1 

In the first place, we must state that closed- 
circuit batteries proper usually consist of a 
glass jar and two elements — carbon and zinc. 
Sometimes a porous cup is used; for what 
reason you will soon learn. 

The chemicals that are used are usually 
different from those used in the open-circuit 
batteries and are much stronger. These 
chemicals are usually sulphuric acid and bi- 

1 The batteries we will now describe are for closed- 
circuit work only, and they are never used for open-circuit 
work. But there is a type of battery made that is avail- 
able for either open or closed circuit operation. This is 
the Edison Primary Battery, which will be described 
later on. 

101 



A-B-C OF ELECTRICITY 



chromate of potash (or chromic acid), which 
are mixed with water. 

We will now examine two of the types of 
closed-circuit batteries, taking first the one 
without the porous cup, of 
which the Grenet is a good 
example. 

This battery, as you see, 
consists of a glass jar, in 
which are placed two plates 
of carbon and one of zinc. 
(Fig. 30.) The latter is be- 
tween the two carbon plates 
and is movable up and 
down, so that it may be 
drawn up out of the solu- 
tion when it is not desired 
to use the battery. When 
the zinc is in the solution 
there is a steady and con- 
tinuous current of electricity developed, which 
can be taken away by wires from the con- 
nections on top of the battery. 

If the zinc were left in the solution when 
the battery was not in use, the acid would 
act upon it almost as much as though the 
electricity were not being used, and thus the 
zinc would be eaten away and the acid 

would be neutralized, so that no more ac- 
102 




Fig. 30 



BATTERIES 



tion could be had when we wanted more 
electricity. 

Now, in the Grenet battery we can light 
a lamp or run a motor for several hours con- 
tinuously, but at the end of that time the 
solution would become black and it would 
do no more work. Then we must throw out 
that solution and put in fresh, and the bat- 
tery will do the same work again, and so on. 

If you should only want to light your lamp 
or run your motor for a few minutes, you 
could pull the zinc up 
from the solution and 
put it down again when 
you wanted the elec- 
tricity once more. The 
carbon element in the 
battery is not consumed 
by the acid, although 
the zinc is. 

Now you will see the 
use of the porous cup. 
We will take as an il- 
lustration of this type 
an ordinary battery in which a porous cup 
is used. (Fig. 31.) 

Here, you will see, the carbon is placed in 
the porous cup, while the zinc is outside in 
the glass jar. In the glass cell with the zinc 

103 




Fig. 31 



A-B-C OF ELECTRICITY 

is usually used water made slightly acid, and 
the strong solution of sulphuric acid and bi- 
chromate of potash (or chromic acid) is 
poured in the porous cup, where the carbon 
is placed. 

The strong solution penetrates the porous 
cup very slowly and gets to the zinc, when it 
immediately produces a current of electricity. 
But the acid does not get at the zinc so freely 
as it does in the battery without a porous cup, 
and, consequently, neither the acid nor the 
zinc is so rapidly used up. 

Where porous cups are used, the batteries 
will give a continuous current for a very much 
longer time than without them, and will, 
sometimes, give many hours' work every day 
for several months without requiring any 
change of solution. 

Polarization. — There is one other reason 
why a longer working time can be had from 
a battery with a porous cup, and that is, in a 
battery without a porous cup the action of the 
acid upon the zinc is so rapid that the carbon 
plates become covered with gas, and, there- 
fore, the proper action by the acid cannot 
take place upon them. Thus, the battery 
ceases to work, and is said to be " polarized/ ; 
When a porous cup is used, the action of the 

acid upon the zinc is slow enough to give off 
104 



BATTERIES 

only a small amount of gas, and thus the acid 
has a chance to act upon the carbon plates 
and develop a steady current of electricity. 

THE WORK DONE BY BATTERIES 

The pressure and quantity of electricity 
given off continuously by open and closed 
circuit batteries is very different. 

The pressure (or " electromotive force") 
of one cell of an ordinary open-circuit battery 
is only about one volt, and the current is 
usually very much less than one ampdre, 
except in a dry cell, which may give more. 

In the closed-circuit batteries described, 
the electromotive force of each cell is about 
two volts, while the current varies from 1 to 
perhaps 50 amperes, according to the size 
of the zinc and carbon plates. 

It would not matter if you made one cell 
as big as a barrel, nor if you put in a dozen 
carbons and zincs, the electromotive force 
would not exceed the volts mentioned for each 
type of battery, but the ampere capacity would 
be greater than in a smaller cell on account 
of the larger size of the carbon and zinc 
plates. 

Internal Resistance. — There is one other 

point which affects the number of amperes 
105 



A-B-C OF ELECTRICITY 

which can be obtained from a closed-circuit 
battery, and that is whether there is a large or 
small internal resistance in the battery itself. 

This depends upon the solution which is 
used and the arrangement of the plates. 

If there is a high resistance in the battery 
itself (called " internal resistance")? the elec- 
tricity must do work to overcome this re- 
sistance before it can get out of the battery 
to do useful work through the wires, and, 
consequently, the capacity in amperes is 
limited. 

If, on the other hand, there is very little 
resistance in the battery, the current has very 
little work to flow to the wires leading from 
the battery, and we can get a larger quantity, 
or greater number of amperes. 

Thus, you will see that while the closed- 
circuit battery is the stronger, and will do 
all that the open-circuit battery will do, and 
even more, in a short time the latter, though 
weaker, will do about as much work for the 
same amount of zinc and carbon as the form- 
er, but takes a much longer time. 

BATTERIES FOR ELECTRIC LIGHT 

As we have explained to you, closed-circuit 
batteries are used for producing incandescent 

106 



BATTERIES 

electric lights in small numbers, as well as 
for running motors. 

To operate incandescent lights, a number of 
batteries connected together are used. The 
number used depends upon the pressure 
which the lamps require to make them give 
the required light. We will now explain 
how the batteries are connected together for 
this purpose. 

Suppose you wished to light an incandes- 
cent lamp of, say, three candle-power, which 
required six volts. We would take three 
closed - circuit batteries which would each 
give two volts, and connect by a piece of 




Fig. 32 



wire the zinc of the first to the carbon of the 
second, and the zinc of the second to the car- 
bon of the third, as shown in the sketch. 
(Fig. 32.) 

We would then attach a wire to the carbon 
of the first and one to the zinc of the third, 
and there would be six volts in these two 

107 



A-B-C OF ELECTRICITY 

wires, which would light up one six-volt 
lamp nicely. 

This is called connecting in series, or for 
intensity. 

Now if each of these cells gave ten amperes 
alone, the three will only give ten amperes 
together when they are connected in series. 

If our lamp only required one ampere, you 
would naturally think that ten similar lamps 
put on the wires would give as good light as 
the one, but that is not so. 

Although you might light up two lamps, 
the pressure would drop and the lights would 
become less brilliant if you put on the whole 
number. So, if we wished to put on the 
whole ten lights we would connect another 
battery and thus increase the pressure, 
which would probably make these ten lamps 
burn brightly. 

These rules hold good for connecting any 
number of batteries for lamps of any number 
of volts — that is to say, there should be cal- 
culated about two volts for each cell and an 
allowance made for drop in pressure. 

CONNECTING IN MULTIPLE 

There is another way of connecting bat- 
teries, and that is to obtain a larger number 

108 



BATTERIES 

of amperes. This is called connecting in 
multiple arc, or for quantity. 

Let us take again for an illustration the 
three cells giving each 2 volts and 10 amperes. 
This time we connect the carbon of the first 
to the carbon of the second, and the carbon 




Fig. 33 

of the second to that of the third; then 
we connect the zinc of the first to that 
of the second, and the zinc of the second 
to that of the third, as shown in the sketch. 
(Fig. 33.) 

We then attach a wire to the zinc and one 
to the carbon in the third cell, and we then 
can obtain from these two wires only 2 volts, 
but 30 amperes. 

There are, again, many ways of connecting 
several o£ these sets together, but it is not 

109 



A-B-C OF ELECTRICITY 

intended in this book to go into these at 
length, for the reason that we only set out 
to give a simple explanation of the first prin- 
ciples of this subject. 

We shall therefore only give an illustra- 
tion of one more method of connecting bat- 
teries which will be easy to understand. This 
is called 

MULTIPLE SERIES 

The sketch we have last given shows three 
batteries connected in multiple. These we 
will call set No. 1. 

Now, suppose we take three more bat- 
teries exactly similar and connect them to- 
gether just in the same manner. Let us call 
this set No. 2. Now take the wire leading 
from the carbon of set No. 2 and connect it 
with the wire leading from the zinc of set 
No. 1. Then take a wire leading from the 
zinc of set No. 2, and a wire leading from the 
carbon of set No. 1, and connect them with 
the lamps or motors. These two sets being 
connected in multiple series, we shall get 4 
volts and 30 amperes. 

This is called connecting in multiple series, 

and may be extended indefinitely with any 

number of batteries. 

We should add that one of the elements in 
no 



BATTERIES 

a battery is called "positive," and the other 
"negative." 



THE EDISON PRIMARY BATTERY 

As this type of battery will work efficiently 
on either open or closed circuit, we have 
thought best to describe it separately at this 
place, in order not to confuse your ideas 
while reading about batteries generally. 

The type of cell we will now describe was 
originated by an inventor named Lalande, 
and was known by that name; but it has 
been greatly improved and rendered more 
efficient by Edison, and is now manufactured 
and sold by him under the name of the 
Edison Primary Battery. 

Before describing the cell itself, let us 
consider the action that takes place in a 
battery of this kind. 

If certain metals are placed in a suitable 
solution, and are connected together, out- 
side of the solution, by wires, vigorous chemi- 
cal action will take place at the surfaces of 
the metals, and electrical energy will be 
produced. The plates must be of different 
metals, and the solution should be one that 
will dissolve neither of them except when 

an electric current is allowed to flow, 
ill 



A-B-C OF ELECTRICITY 

One of the metals is usually zinc, which 
is gradually eaten away or dissolved by the 
solution while the battery is delivering elec- 
trical energy. It is the chemical combina- 
tion of the zinc and the solution that produces 
this energy, which leaves the zinc in the form 
of an electric current, and passes through 
the solution to the other metal, out of the 
cell to the wire, and thence back by another 
wire to the zinc, where it is once more started 
on its circuit. 

At the surface of the other metal, which 
may be, and frequently is, copper, small bub- 
bles of the gas called hydrogen are produced. 
This gas rises to the surface of the liquid and 
gradually passes off into the air. But its 
presence offers resistance to the passage of 
the current; so that generally there is as- 
sociated with the copper a supply of the gas 
oxygen. Oxygen and hydrogen are always 
very eager to mix with each other, and, 
therefore, when the hydrogen bubbles appear 
they are quickly taken up by the oxygen 
near by. The mixture of these two gases 
forms water, which becomes part of the solu- 
tion. All of this happens so quickly that the 
hydrogen cannot be perceived so long as 
there is any oxygen left in the copper-oxide 
plate. 

112 



BATTERIES 




In the Edison Primary Battery (Fig. 34) 
the plates are zinc, known as the negative, 
and copper oxide (copper and oxygen), or 
the positive. These are suspended in a solu- 
tion of caustic soda and 
water, the plates and solu- 
tion being contained in jars 
of glass or porcelain. The 
plates are provided with 
suitable wires for connect- 
ing the cells with one an- 
other and with the lamps, 
motors, or other devices 
which they are to operate. 
There are usually two zinc 
plates and one copper-oxide 
plate, or multiples thereof. The quantity of 
current that may be withdrawn depends on 
the size and number of the plates, as well as 
upon their construction and arrangement. 

The voltage of these cells is low, being 
about 0.65 volt each; but this is more than 
compensated for by the fact that the internal 
resistance of the battery is so low that the 
voltage is not perceptibly affected even at 
continuous high-discharge rates, and that the 
voltage remains practically constant through- 
out the life of the cell. 

Furthermore, when the battery is not in 

8 113 



Fig. 34 



A-B-C OF ELECTRICITY 

use there is practically no local action. Con- 
sequently, the cells may remain on open cir- 
cuit (that is, doing no work) for years and 
there will be no loss of energy. The cell 
will then operate with the same practical 
efficiency as if it were new. In some classes 
of work this battery remains in service from 
four to six years without attention. 

Another peculiar advantage of this bat- 
tery lies in the fact that the plates and the 
electrolyte are so well proportioned that they 
are all exhausted at the same time, and then 
new plates and solution can be put in the 
jar, restoring it to its original condition. 
These batteries are used in great numbers 
for railway signal work and for other pur- 
poses, such as fire and burglar alarm sys- 
tems, various telephone functions, operation 
of electric self-winding and programme clock 
systems, small electric-motor work, for low 
candle-power electric lamps, gas-engine ig- 
nition, electro-plating, telegraph systems, 
chemical analysis, and other experimental 
work where batteries are required that will 
remain in use for long periods of time without 
requiring any attention or renewal. 

The remarks that have been made on 
previous pages about connecting up batteries 
in series, multiple, and multiple series apply 

114 



BATTERIES 

also to these Edison Primary Cells. Fig. 
35 shows a battery of four of these cells con- 
nected in series. 



SECONDARY, OR STORAGE, BATTERIES 

The open and closed circuit batteries we 
have so far described are used to produce 
electricity by the 
action of the 
chemicals upon 
the elements 
contained in 
them. They are 
called primary 
batteries. 

The batteries 
which we will 
now tell you of 
are called sec- 
ondary, or stor- 
age, batteries, and do not of themselves 
make any primary current, but simply act 
as reservoirs, so to speak, to hold the energy 
of the electric current which is led into 
them from a dynamo or primary battery. 
At the proper time and under proper 
conditions these secondary batteries will 
give back a large percentage of the energy 

115 




Fig. 35 



A-B-C OP ELECTRICITY 

of the electric current which has been stored 
in them. 

This class of battery has been called by 
these three names: " secondary battery/ ' 
" accumulator/ ? and " storage battery"; but 
as the latter name is used almost exclusively 
in this country, we shall use it in the following 
description. 

TWO TYPES 

There are two distinct types of storage bat- 
tery. One is called the "lead" or "acid" 
storage battery, and the other the "alkaline" 
or "nickel-iron" storage battery. Each of 
them simply acts as a reservoir to hold the 
energy of the electric current which is led into 
it, and each of them, under proper conditions, 
will give back that energy. As the lead 
storage battery is the oldest in point of dis- 
covery and invention, we will describe it first. 

THE LEAD STORAGE BATTERY 

A lead storage battery usually consists of 
a glass or hard-rubber jar containing lead 
plates and a solution consisting of water and 
sulphuric acid. A single unit is usually 
called a "cell." (Fig. 36.) 

There are always at least two lead plates 

116 



BATTERIES 



in a storage-battery cell of this kind, although 
N there may be any number above that. For 
the sake of making 
a clearer expla- 
nation to you, we 
will take as an illus- 
tration a cell con- 
taining only two 
plates. 1 

We have, then, a 
glass or hard-rubber 
jar containing two 
lead plates and a 
solution consisting 
of water and sul- 
phuric acid. These 
plates are called the 
" elements, " and one 

is called the positive and the other the nega- 
tive element. The solution is called the 
" electrolyte." 

The positive element is a sheet of lead upon 
which is spread a paste made of red-lead. 
The negative element is a similar sheet of lead 
upon which is spread a paste made of litharge. 

1 Practically, there is always one more negative plate 
than positive plates in a regular storage-battery cell. 
Consequently, , a standard cell always contains an odd 
number of plates. 

117 




Fig. 36 



A-B-C OF ELECTRICITY 

Now, when these plates are thus prepared, 
they are put into the acid solution in the 
jar, and a wire attached to each plate is con- 
nected with the two wires from a dynamo 
or other source of electric current, just as a 
lamp would be connected. 

The electric current then goes into the 
storage-battery cell, entering by the positive 
plate and coming out by the negative. These 
plates and the paste upon them offer some 
resistance, or opposition, to the passage of 
the current, so the electricity must do some 
work to get from one to the other. The work 
it does in this case is to so act upon the paste 
that its chemical nature is changed. 

So, after the primary current has been 
passed from one plate to the other for some 
time, and after several " discharges," the 
storage battery may be disconnected, being 
now " formed." 

The paste on the lead plates is now found 
to have changed its chemical nature, the 
paste on the positive plate having been trans- 
formed into peroxide of lead, and that on 
the negative plate into spongy lead. On 
arriving at this condition, the paste on the 
plates is called " active material." 

This process of " formation" is absolutely 
essential before the lead storage battery is 

118 



BATTERIES 

ready to be used for actual work. So, 
when the plates have been fully "formed," 
the storage battery may be again connected 
with a source of electric current which again 
enters by the positive plate and leaves by 
the negative. This current so acts on the 
active material that it combines with the 
acid solution and, through the energy of the 
charging current, forms other chemical com- 
pounds which may for convenience be called 
1 1 sulphates." When the charging current has 
flowed through the battery long enough to 
produce these changes in the active material 
the battery is said to be "charged," and is 
ready for useful work. 

If the two wires attached to the plates 
are now connected with electric lamps, or a 
motor, or other device, the active material 
will develop energy in the effort to again 
change its nature. This energy takes the 
form of an electric current, which leaves the 
battery and passes through the conductors 
and operates the lamps, motors, or other de- 
vices in its passage. 

In this way the battery is said to be "dis- 
charged," and at the end of its discharge it can 
again be charged and discharged in a similar 
manner for a long time, until the active ma- 
terial is either used up or drops off the plates. 

119 



A-B-C OF ELECTRICITY 

So far as the actual details of construction 
are concerned, lead storage batteries are 
made in a great many different ways, but 
the materials are, in general, of the same 
nature as those we have mentioned above. 



THE ALKALINE STORAGE BATTERY 

We shall now describe an entirely different 
type of storage battery, which contains 
neither lead nor acid. It is one of the many 
inventions of Thomas A. Edison. 

In the alkaline storage battery the gas 
called oxygen plays a very important part, 
and we will try to make it clear to you what 
this part is. 

You are well aware of the fact that if you 
leave your pocket-knife out in the air it will 
get rusty. The reason for this is that iron 
or steel quickly tends to combine with the 
oxygen of the air, and this combination of 
oxygen and iron is rust, otherwise called 
oxide of iron, or iron oxide. 

This iron oxide, or rust, is therefore the 
result of a chemical action between the iron 
and the oxygen. 

Now as all chemical actions require the 
expenditure of energy, there has been de- 
veloped either heat or electricity in the proc- 
120 



BATTERIES 

ess. The oxygen may be taken away from 
the iron oxide, chemically; but here again 
would be another chemical action which 
would require energy to be once more ex- 
pended. 

Iron oxide may be made chemically in 
many different ways. It is frequently made 
in the form of a powder. Therefore, we do 
not have to depend upon iron rust for a 
supply of this material. 

Before going further we must consider 
another oxide — namely, nickel oxide. It is 
characteristic of nickel that when it is com- 
bined with oxygen to a certain degree so as 
to form the compound known as nickel 
oxide, it will receive still more oxygen. 

Now, if under proper conditions we com- 
pel iron oxide to give up its oxygen to some 
other kind of chemical compound, such as 
nickel oxide, we must expend energy. But, 
on the other hand, if this nickel oxide gives 
back the oxygen to the iron — which it will do 
if opportunity is given — there is energy pro- 
duced again in receiving the oxygen. In 
other words, the energy previously expended, 
or part of it, is now returned. 

This action and reaction are practically 
those that take place in the Edison alkaline 
storage battery. For simplicity of illustra- 

121 



A-B-C OF ELECTRICITY 



tion we will consider a cell containing only- 
two plates, one positive and one negative. 

The negative plate is made up of a number 
of small, flat, perforated pockets containing 
iron oxide in the form of a fine powder. The 
positive plate is made 
up of small, perforated 
tubes containing nickel 
oxide mixed with very 
thin flakes of metallic 
nickel. (Fig. 37 illus- 
trates these plates, the 
positive being in front.) 
These two elements, 
positive and negative, 
having wires or con- 
ductors attached, are 
placed in a nickeled- 
steel can containing the 
electrolyte, which con- 
sists of a potash solu- 
tion. You will see that 
this differs from a lead storage battery, in 
which the electrolyte is sulphuric acid and 
water. If we were to put this acid solution 
into a metallic can (except one made of lead) 
the can would not last long, as the acid would 
quickly eat holes through it. 

Now let us see what takes place in the 

122 




Fig. 37 



BATTERIES 

Edison alkaline storage battery. If an elec- 
tric current from a dynamo or other source 
of electricity is caused to pass through the 
positive to the negative plate the oxygen 
present in the iron oxide passes to and re- 
mains with the nickel oxide. During all the 
time this is going on the battery is said to 
be " charging/ ' and when all the oxygen has 
been removed from the iron oxide and is 
taken up by the nickel oxide, then the bat- 
tery is said to be "charged," and the flow of 
current into the battery is stopped. 

A change has now taken place. The 
powder in the negative plate is no longer 
iron oxide, but has been reduced to metallic 
iron, because the oxygen has been removed. 
The powder in the positive plate is now 
raised to a higher or super oxide of nickel, 
because it has taken the oxygen that was in 
the iron. 

But the nickel oxide will readily give up 
its excess of oxygen, and the iron will receive 
it back freely if permitted. If the proper 
conditions are established, this transfer of 
oxygen will take place, but the iron cannot 
receive it without delivering energy. 

The proper conditions are established by 
providing a conducting circuit between the 
two elements, in which lamps, motors, or 

123 



A-B-C OF ELECTRICITY 



other electrical devices are placed. As soon 
as this circuit is provided, the opportunity 
is given to the iron to receive the oxygen. 
This it does, and in so doing develops elec- 
trical energy. 

This energy is in the form of electric cur- 
rent which is then delivered by the battery 
on what is called the " discharge/ ' and this 
current may be used for light- 
ing lamps or for operating 
motors or other electrical de- 
vices. 

The battery is said to be 
discharging as long as the iron 
is receiving oxygen from the 
nickel oxide. As soon as it 
becomes iron oxide once more, 
the giving out of energy ceases 
and the battery is said to be 
" discharged/' and must again 
be charged to obtain further 
work from it. Such a battery 
can be charged and discharged 
an indefinite number of times. 
This type of battery is very rugged, and 
its combinations are not self-destructive. It 
is very simple, as it provides chiefly for the 
movement of the oxygen back and forth; 
besides, it gives much more current for its 

124 




BATTERIES 

weight than the lead type of storage battery. 
(Fig. 38 shows the plates of a standard Edi- 
son cell removed from container.) 

CONNECTING STORAGE BATTERIES 

On the discharge, one cell of a lead stor- 
age battery gives an average of about 2 
volts, and a cell of alkaline storage battery 
about 1.2 volts, no matter what its size 
or the number of plates may be. When 
there are more than two plates in one cell, 
all the positives in that cell are connected 
together by metallic strips or bands, and 
all negatives in the cell are connected to- 
gether in a similar way. 

Although we cannot obtain more than the 
above-named electromotive force from one 
cell of either type of storage battery, we can 
obtain a greater ampere capacity by using 
large plates instead of small ones, or by 
using a larger number of small size. 

The same effects are produced by con- 
necting the cells in series, or multiple, or 
multiple series, as we showed you in re- 
gard to primary batteries; and the storage 
batteries may be charged as well as dis- 
charged when connected in any one of these 
ways. 

125 



A-B-C OF ELECTRICITY 

CHARGING CURRENT 

The current which is used for charging 
must always be greater in pressure than that 
of the storage batteries which are being 
charged. If it is not, the storage batteries 
will be the stronger of the two and will over- 
power the charging current and so discharge 
themselves. 



X 

CONCLUSION 

WE will now bring this little volume to a 
close, having given you a brief outline 
of the simplest rudiments of that wonderful 
power of nature, Electricity. 

We may compare this subject to a beauti- 
ful house the inside of which you would like 
to examine from top to bottom. We have 
opened the door for you; now walk in and 
examine everything. There may be a great 
many stairs to climb, but what you see and 
learn will repay for all the trouble. 



THE END 



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